Antiviral immunity(Prepared by Inzhevatkina S.M.,

Department of Microbiology and Virology of Russian National Research Medical University NI Pirogov)

Antiviral immunity is subdivided into two categories:

1. innate antiviral immunity (including surface anatomical barriers, humoral and cell-mediated immunity);

2. adaptive antiviral immunity (including adaptive antiviral immunity (including both humoral and cell-mediated immunity).

Both innate and adaptive immunity depend on the ability of the immune system to distinguish between self and non-self (foreign) substances.

Types of immunity

Innate antiviral immunity

Characteristic features

1. Response is non-specific

2. Exposure leads to immediate maximal

response

3. It contains cell-mediated and humoral components

4. It lacks immunological memory

5. It is found in nearly all forms of life

Innate antiviral immunityincludes natural protective barriers (surface anatomical barriers) of the body (skin, mucus, mucociliary clearance, gastric acid, tears, bile), and antigen-nonspecific immune response (interferons, other cytokines, natural killer cells (NK-cells), macrophages, dendritic cells, Toll-like receptors, complement components, α-defensins, apoprotein B RNA-editing enzyme (APOBEC3G), fever), which occurs very quickly (within hours) and control and limit local viral replication and spread.

Surface Barriers or Mucosal Antiviral Immunity

The first and most important barrier is the skin. The skin cannot be penetrated by most viruses(except dermatotrophic viruses) unless it already has an opening, such as a nick, bite, scratch, cut, etc.

Mechanically, viruses are expelled from the lungs by ciliary action as the tiny hairs move in an upward motion; coughing and sneezing abruptly eject both motion; coughing and sneezing abruptly eject both living and nonliving things from the respiratory system; the flushing action of tears, saliva, and urine also force out pathogens, as does the sloughing off of skin. In damage, especially from smoking, results in increased frequency of viral respiratory tract infection, especially influenza.

The stomach is a formidable obstacle insofar as its mucosa secrete hydrochloric acid (0.9 < pH < 3.0, very acidic) and protein-digesting enzymes that kill many pathogens.

Fever can limit the replication or directly inactivate the virus particles, particularly enveloped viruses, which are more sensitive than nonenveloped viruses. Several host immune mechanisms might also be expected to be more active at also be expected to be more active at higher temperatures: complement activation, lymphocyte proliferation and the synthesis of cytokines and antibody.

Protection by elevated temperature or antibody administered before

or after intracerebral infection with the picornavirus.

α-defensins are the family of positively charged

peptides which has antiviral activity. Defensins (low

molecular weight proteins) found on the skin, in the

lung and nasal passages, genitourinary and

gastrointestinal tracts have antimicrobial activity. They

are classified into α-defensins and β-defensins. The

Paneth cells localized in the crypts of the small

intestine beneath the epithelial stem cells produce intestine beneath the epithelial stem cells produce

antibacterial and antifungal peptides called cryptdins

(α-defensins). They can interfere with human

immunodeficiency virus (HIV) and block entry of the

virus into the cell by binding to the CXCR4 cellular

receptor. Thus, some people have prolonged

incubation period of acquired immunodeficiency

syndrome.

In the absence of serum (such as at mucosal surfaces), α-defensins inactivate enveloped virus particles by disrupting viral envelopes or by

interacting with viral glycoproteins, such as HIV gp120.

Apoprotein B RNA-editing enzyme (APOBEC3G) ensures the innate host defenses against retroviral infection, because it induces hypermutation in retroviral DNA by deaminating cytosines in both mRNA and retroviral DNA. both mRNA and retroviral DNA. Inactivation of these molecules reduces infectivity of HIV.

Complement systemThe complement system is a biochemical cascade that

helps clear pathogens from an organism. It belongs to the innate immune system. However, it can be recruited and brought into action by the adaptive immune system.

The complement system consists of a number of small proteins found in the blood, normally circulating as inactive zymogens. When stimulated by one of several triggers, proteases in the system cleave specific proteins to release cytokines and initiate an amplifying cascade of further cytokines and initiate an amplifying cascade of further cleavages. The end-result of this activation cascade is massive amplification of the response and activation of the cell-killing membrane attack complex (MAC). The MAC can be deposited on many viruses, virus-infected cells, fungi, bacteria, and other cells.

Over 30 proteins and protein fragments make up the complement system, including serum proteins, serosal proteins, and cell membrane receptors. These proteins are synthesized mainly in the liver, and they account for about 5% of the globulin fraction of blood serum.

Figure 2Figure 2--2121Complement system

Figure 2Figure 2--2222

Figure 2Figure 2--3535

Macrophages, especially fixed macrophages of the reticuloendotelial system and alveolar macrophages, are the important cell types in limiting viral infection. They are efficient killers of virally infected cells. Also macrophages filter viral infected cells. Also macrophages filter viral particles from blood (especially Kupffer cells) and inactivate opsonized viral particles. Polymorphonuclear leukocytes are insignificant in antiviral protection.

Classification of macrophages

Examples of macrophages

Examples of microphages

Possible Outcomes of Phagocytosis of a Virus

Natural killer cells (NK-cells) are large granular lymphocytes which lack T-cell receptor, CD3 proteins and surface IgM and IgD. They constitute 5% to 10% of peripheral lymphocytes. They are named “natural” killer cells because they named “natural” killer cells because they are active without prior exposure to the virus, are not enhanced by exposure, and are not specific for any virus. NK-cells lack immunologic memory.

Natural killer cells (NK-cells)

NK-cells are stimulated by wide spectrum of cytokines, such as interleukins (IL-2, IL-12, IL-15, and IL-18), IFN-α, IFN-β, and TNF-α. They can kill without antibody, but IgG improves their effectiveness, a process called antibody-dependent cellular cytotoxicity (ADCC). NK-cells express several receptors, similar to surface markers of T-cell, including similar to surface markers of T-cell, including IL-2 receptor, Fas ligand, Fc-receptor for IgG, and complement receptors for ADCC. NK-cells provide an early cellular response to a viral infection, have antitumour activity, and amplify inflammatory response after bacterial infections. Activated NK-cells produce IFN-γ and IL-1.

The granules in an NK-cell contain perforin, a pore-forming protein, and granzymes (esterases), which are similar to the contents of the granules of a CD8 cytotoxic T-lymphocyte. A synapse (pocket) is formed between NK-cell and target cell, and perforin and granzymes are released to disrupt the target cell and induce apoptosis. The interaction of the Fas ligand on the NK cell with Fas protein on the target cell can also induce apoptosis.

Some viruses inhibit MHC class I expression on the cells they infect. NK-cells have receptors that detect the presence of the I MHC class proteins on the cell surface. If a cell has enough I MHC molecules, the cell is not killed by NK-cells. If there is insufficient MHC class I on the surface, the receptor is not engaged and the NK-cells are activated to kill the target cells.

Scheme of action of NK cells

Toll-like-receptors

Toll-like-receptors on macrophages and

other cells bind viral double-stranded RNA,

DNA, and some other viral glycoproteins. This

process leads to release of proinflammatory

cytokines such as TNF-α, IL-1 or IL-6. cytokines such as TNF-α, IL-1 or IL-6.

Signalling through the Toll-like receptors also

leads to an increased expression of MHC

molecules and co-stimulatory molecules, thus

enhancing antigen presentation and usually

leading to the activation of T-helper cells.

Five TLRs are involved in anti-viral responses: TLR4 senses F protein from respiratory syncytial virus (RSV) (TLR4 can be activates also by bacter ial LPS); double-stranded RNA (polyI:C) is sensed by TLR3; TLR9 senses viral CpG DNA; and TLR7 (human only) and TLR8(human and mouse) sense single-stranded viral RNA (ssRNA).

Interferons (IFNs) are a heterogenic group of glycoproteins. Their production is induced by viral infection or exposure to other stimuli (double-stranded RNA, intracellular bacteria, bacterial endotoxins, tilorone, etc.). IFNs are members of large cytokine family, which inhibit viral cytokine family, which inhibit viral replication by blocking the translation of viral proteins. Also IFNs block the growth of certain cancer cells, bacteria, and protozoa.

Production of virus, interferon, and antibody during experimental infection of humans

with influenza wild-type virus

1. Classical IFNs are divided into three groups based on the cell of origin, namely, leukocyte, fibroblast, and lymphocyte. They are designated as IFN-α, IFN-β, and IFN-γ, respectively.

Properties of Interferons

But IFN- λ is described from 2003 (newest type of IFN, which is not completely investigated).

2. The different IFNs are similar in size, but all classes of IFNs are antigenically distinct.

3. The IFN gene families have diverged so that the coding sequences now are not closely related.

4. IFN-α and IFN-β are resistant to low pH.

5. IFN-β and IFN-γ are glycosylated, but the sugars are not necessary for biologic activity, so cloned IFNs produced

Properties of Interferons

biologic activity, so cloned IFNs produced in bacteria are biologically active.

6. IFN-α and IFN-β participate in innate immunity and designated as type I IFN; whereas IFN-γ is responsible for adaptive immune response and designated as type II or immune IFN.

Induction of IFN-β, IFN-α, and IFN-γby foreign nucleic acids, foreign cells,

and foreign antigens.

INFs are species-specific in function; thus, INFs produced by human cells are active only in human cells but not effective in cells of other species.

The inhibitory action of IFNs is not specific for any particular virus; IFNs added to cells prior to viral infection cause marked selective inhibition of viral replication but practically have no effect on of viral replication but practically have no effect on cell functions.

IFNs are highly potent (typical feature of cytokines), so very small amounts are necessary for their function.

Several recombinant IFN preparations are used in clinical practice to prevent viral diseases despite side effects of such drugs.

IFNs are produced within a few hours of the initiation of viral replication and ensure the early protective mechanism against viral spread.

The prolonged list of interferon production stimuli shows that induction of IFN-α and IFN-β (type I IFN) is not specific. Both IFNs need the same receptor for activation. same receptor for activation.

IFN-γ (type II, or immune IFN) recognizes a different receptor. Receptor binding triggers tyrosine phosphorylation and activation of transcription factors in the cytoplasm, which then translocates into the nucleus and mediate transcription of IFN-inducible genes within minutes after IFN binding.

Then several enzymes are initiated:1) a dsRNA-dependent protein kinase, which

phosphorylates and inactivates cellular initiation factor eIF-2 and thus prevents formation of the initiation complex needed for viral protein synthesis;

2) an oligonucleotide-synthetase which activates a cellular endonuclease, ribonuclease, which in turn degrades viral mRNA;

3) a phophodiesterase, which inhibits peptide chain elongation;elongation;

4) nitric oxide synthase, which is induced by IFN-γ in macrophages for adaptive (specific) immune response. Other steps in viral replication may also be inhibited by interferon.

Thus, IFNs have no direct effect on extracellular virus particles but act via binding to a receptor on cell surface that involves the cellular synthesis of enumerated antiviral enzymes.

Mechanism of Action of IFNs

IFNs stimulate cell-mediated immunity by activating effector cells and enhancing recognition of the virally infected target cell.IFNs stimulate pre-NK cells to differentiate to NK-cells to activate an early, local, innate defense against infection. Activation of macrophages by infection. Activation of macrophages by IFN-γ promotes production of more IFN, secretion of other biologic response modifiers, phagocytosis, recruitment, and inflammatory responses. IFN-γ increases the expression of class II MHC antigens on macrophage to help promote antigen presentation to T-cells.

Interferon-lambda (IFN- λ)IFN- λ had been described in 2003. There are 3 IFN- λ

genes that encode 3 distinct but highly related proteins

denoted IFN- λ1, - λ2, and – λ3. These proteins are also

known as interleukin-29 (IL-29), IL-28A, and IL-28B,

respectively. Collectively, these 3 cytokines comprise the type

III subset of IFNs. They are distinct from both type I and type

II IFNs for a number of reasons, including the fact that they II IFNs for a number of reasons, including the fact that they

signal through a heterodimeric receptor complex that is

different from the receptors used by type I or type II IFNs. Although type I IFNs (IFN-alpha/beta) and type III IFNs (IFN-

lambda) signal via distinct receptor complexes, they activate

the same intracellular signaling pathway and many of the

same biological activities, including antiviral activity, in a wide

variety of target cells.

Genetics of Interferon-lambda (IFN- λ)

All the genes of the type III family are clustered on chromosome 19 in human clustered on chromosome 19 in human and consist of several exons (5 exons for IFN- λ1, 6 for IFN- λ2 and IFN- λ3), whereas the genes for type I IFNs members are clustered on chromosome 9 and are composed of a single exon.

Interferon-lambda (IFN- λ)Consistent with their antiviral activity,

expression of the IFN-lambda genes and their

corresponding proteins is inducible by infection

with many types of viruses. Therefore, expression

of the type III IFNs (IFN-lambdas) and their

primary biological activity are very similar to the primary biological activity are very similar to the

type I IFNs. However, unlike IFN-alpha receptors

which are broadly expressed on most cell types,

including leukocytes, IFN-lambda receptors are

largely restricted to cells of epithelial origin.

Targets of IFN- λ

IFN-lambdas inhibits the replication of

different virus species such as encephalomyocarditis virus, vesicular stomatitis virus, cytomegalovirus, herpes simplex virus, and influenza A virus.

III IFNs were restricted in the repertoires and

were less strong in the potency than type I IFNs.

The reason why type III IFNs have less and

even no anti-viral activity in some cases is partly

due to low or limited expression of the receptor

complexes.

Clinical application of IFN- λAdenoviruses bearing IFN-lambda gene

could produce large amounts of IFN-lambda in the infected tumors, which makes the local concentrations high in the microenvironment and subsequently can produce better anti-and subsequently can produce better antitumor effects in combination with anti-cancer agents. Further preclinical studies regarding the

therapeutic effects are required and high

transduction efficacy by adenoviruses or other

vector systems is one of the crucial factors to make

the clinical application feasible as suggested in

other cases of cancer gene therapy.

The importance of interferon in the response to certain natural virus infections varies. Much depends on the

effectiveness of the virus in stimulating interferon

production and on its susceptibility to the antiviral action of

interferon. Interferon protects solid tissues during virus infection; it is also disseminated through the

bloodstream during viremia, thereby protecting distant organs against the spreading infection. Cells protected

against viral replication may eliminate virus by degrading against viral replication may eliminate virus by degrading

the virus genome.

Drugs, prepared from recombinant interferons

A number of cytokines, known collectively as

proinflammatory cytokines because they accelerateinflammation, caused by viruses. also regulate

inflammatory reactions either directly or by their ability toinduce the synthesis of cellular adhesion molecules orother cytokines in certain cell types. The major

proinflammatory cytokines that are responsible for early

responses are IL-1α IL1-β IL-6 and TNF-α Other pro-responses are IL-1α, IL1-β, IL-6, and TNF-α. Other pro-

inflammatory mediators include IFN-γ, IL-8, IL-11,IL-12, IL-

17, IL-18 and a variety of other chemokines that

chemoattract inflammatory cells, and various

neuromodulatory factors. The net effect of an inflammatory

response is determined by the balance between

proinflammatory cytokines and antiinflammatorycytokines (IL-4, IL-10, IL-13, IL-16, IFN-α).

Proinflammatory and Antiinflammatory Cytokines

Adaptive immune system

Characteristic features

1. It induces pathogen and antigen specific response

2. It has lag time between exposure and maximal responsemaximal response

3. It forms cell-mediated and humoralcomponents

4. Exposure leads to immunological memory

5. It is found only in jawed vertebrates

Adaptive immune response is subdivided into humoral immunity and cellular (cell-mediated) immunity. Active acquired immunity can be elicited by contracting the symptomatic disease, by suffering from inapparent infection, or by being vaccinated. The first exposure to a virus stimulates the production of antibodies and the activation of cytotoxic T lymphocytes. the activation of cytotoxic T-lymphocytes. Practically all capsid proteins of naked viruses and the glycoproteins of enveloped viruses are foreign to the host and can be immunogenic. But the protective activity of antibodies varies from virus to virus.

Adaptive Immunity

Role of Antibodies in Antiviral Immunity

In mediating humoral antiviral immunity the important classes of are IgM, IgG and IgA. IgM and IgG play a major role in blood and tissue spaces, major role in blood and tissue spaces, IgA (secretory IgA) is more important on mucosal surfaces (for example, protection of IgA against most respiratory viruses lasts more than 5 years).

Formation of humoral

immune response

Comparison of Primary and Secondary Immune Response

Primary and Secondary Immune

responses (IgM and IgG production)

Primary and Secondary Immune

responses (IgM and IgG production) Example

Structure of antibodies

Functions of antibodies1. They prevent absorption of the virus on cell

receptors by neutralization of surface proteins.

2. They enhance virus degradation.

3. They prevent release of the virus progeny from infected cells.

4. They can cross-link viral proteins and stabilize the virus, thus, viral uncoating does not occur and virus can’t replicateand virus can’t replicate.

5. Antibody-coated viruses more rapidly phagocytized.

6. Lysis of virus-infected cells in the presence of antibody and complement. Antibodies bind to the virus-specific antigens on the cell surface & then bind complement which enzymatically degrades the cell membrane. Thus, the cell is killed before the full viral reproduction is finished, and the spread of the virus is significantly reduced.

Particular Features of Antiviral Antibodies

Not all antibodies can neutralize viral

infectivity. Antibodies to internal antigens of virus are non-neutralizing. Antibodies to

surface antigens vary in their activity. For surface antigens vary in their activity.

example, influenza virus has two types of

surface antigens – hemagglutinin and

neuraminidase. The former can neutralize

infectivity, but the latter cannot. But anti-

neuraminidase antibody can inhibit the release

of the progeny virions from infected cells.

In some cases antibodies can paradoxically enhance the severity of infection.

1. They form immune complexes. Most extrahepatitic lesions of type B hepatitis is due to damage caused by immune complexes.

2. They enhance the severity of respiratory syncitial virus in early infancy is believed due the presence of passively acquired maternal antibodies. In elder children, who lack maternal antibodies, the infection is mild. is mild.

3. The phenomenon of “original antigenic sin”. It means that if a person is exposed to a virus (e.g., by vaccination), which cross-reacts with the another virus (which causes current epidemical outbreak), more antibody may be produced against the first, original virus (vaccine strain of influenza virus), then against the second, current one (epidemical strain of influenza virus), thus, inducing more severe disease (influenza) than it can be without any vaccination.

Cytotoxic T-lymphocytes (CTLs)Lysis of virus-infected cells is also caused by CD8-

positive cytotoxic T-lymphocytes (CTLs). CTLs recognize viral antigen on virus-infected cells only in association of I MHC molecules. CTLs kill infected cells by three ways:

1) by releasing perforins, which make holes in the cell membrane of the target;

2) by releasing proteolytic enzymes called into 2) by releasing proteolytic enzymes called granzymes into the infected cells, which degrade the cell content;

3) by interaction of Fas ligand protein on CTLs with Fas protein on the target cells, resulting in apoptosis (programmed cell death). Killing by CTLs the virus-infected cells eliminates the source of new virus.

Cell-mediated immunity is especially important for resolving infection by syncytia-forming viruses (measles, varicella-zoster, and herpes simplex viruses).

Cytotoxic T-lymphocytes(CTLs)

Killing of Virus-infected Cells by CTLs

Functions of Proteins in Lytic Granules of CTLs

Figure 1Figure 1--2525Killing of Virus-infected Cells by CTLs

ADCCIn addition of direct killing by cytotoxic

T-cells, virus-infected cells can be destroyed by combination of IgG and phagocytic or NK-cells. In the process of antibody-dependent cellular cytotoxicity antibody-dependent cellular cytotoxicity (ADCC), antibody (IgG) bound to the surface of the infected cells is recognized by IgG receptors on the surface of phagocytic cell (macrophages) or NK-cell, & the virus-infected cell is killed.

Antiviral Therapy

The key to successful prevention & treatment of viral disease is antiviral specificity. An effective antiviral agent must impair the ability if the virus to replicate & spread while sparing the host cells themselves.

The main types of antiviral preparations are:

1. Immunoglobulins;

2. Interferons;

3. Antiviral drugs.

Antiviral Immunoglobulins

Specific antiviral immunoglobulins contain neutralizing antibodies, which bind and coat the virion. Such treatment is called passive immunization and effective only during 3-4 days after entry of viruses in the host (during the first 3-4 of incubation period) . But there are several limitations to the use of immunoglobulins.

1. Many serums are not readily available in large 1. Many serums are not readily available in large amounts.

2. Sera may be contaminated with viruses or other infectious agents.

3. The successful prophylaxis depends on early recognition of exposure, not later than 3-4 days after exposure. Administration of sera is generally useless when symptoms of infection appear.

Specific antiviral immunoglobulinscan prevent measles, varicella, rabies, hepatitis A, hepatitis B, tick-borne encephalitis, Japanese encephalitis, rubella, cytomegalovirus infection etc. It’s better to treat by antiviral immunoglobulins better to treat by antiviral immunoglobulins obtained from humans.

Antibodies of animal origin (from horses, bullocks or goats) ought to be tested for allergic reactions before inoculation.

InterferonsInterferons are now manufactured by

biotechnology in many countries for different purposes, including antiviral therapy. Recombinant α–interferons are widely used for treatment of chronic hepatitis B and C infection, Kaposi’s sarcoma caused by herpesvirus 8 and papillimavirus infection. But they have very short half-life and many side effects, most commonly systemic (flu like symptoms of fever, myalgia commonly systemic (flu-like symptoms of fever, myalgia and headache) and hematologic (leukopenia and thrombocytopenia). Modifications of interferons by addition of polyethylene glycol (peginterferon) results in longer half-life than unconjugated interferon and is administered once a week. Artificial interferon inducers are also used for treatment of chronic hepatitis B and C infection.

Antiviral Drugs

The activity of most antiviral drugs is limited to a specific family of viruses. Compared with the drugs for treatment of bacterial infections, the number of antiviral drugs is very limited. The main target drugs is very limited. The main target stages of viral life cycle for antiviral drugs include attachment of virus to host cells; uncoating of viral genome; viral nucleic acid synthesis; translation of viral proteins; assembly of virion; and release of the progeny virus particles.

Practically about a half of all antiviral targets are nucleoside (or nucleotide) analogues, which are nucleosides with modifications of the base, sugar, or both. They inhibit nucleic acid replication by inhibition of polymerases for nucleic acid replication. The most effective analogues are those able to specifically inhibit virus-encoded enzymes, with minimal inhibition of analogous host cell enzymes, because viral enzymes are less enzymes, because viral enzymes are less accurate than host cell enzyme. Binding of modified nucleoside (analogue) to viral enzyme is several hundred times better than the host cell enzyme. Antiviral drug that cause termination of the DNA chain by means of modified nucleoside sugar residues include acyclovir (acycloguanosine), gancyclovir, valacyclovir, pencyclovir, famcyclovir for herpesviral infections.

Modified nucleoside sugar residues include acyclovir which possesses three-carbon

fragment instead of carbohydrate ring but

Non-nucleoside reverse transcriptase inhibitors (nevirapine, delavirdine, and efavirenz) act as non-competitive inhibitors of HIV-1 reverse transcriptase by binding to a hydrophobic pocket proximal to the enzyme catalytic pocket proximal to the enzyme catalytic site. It induces conformational changes which inhibits the synthesis of viral DNA. But these drugs are inactive against HIV-2.

Penetration and uncoating of several viruses can be prevented for several viral infections. For example, absorption and

penetration of influenza A virus through

endocytic vacuoles occur normally. Fusion of

viral envelope can be effective only at low pH.

Amantadine and rimantadine raise pH in

intracellular vacuoles and block an ion channel intracellular vacuoles and block an ion channel

formed by the integral membrane protein (M2) of

influenza A virus, but not influenza B virus. Thus,

transcription by the virion RNA polymerase does

not take place, because uncoating cannot occur.

The Major Sites of

Antiviral Drug Action

Specific Prophylaxis of Viral Infections

Prevention of viral infections is by vaccination. There are several types of viral vaccines

1. Live (attenuated) vaccine. Live virus particles with very low virulence are particles with very low virulence are administered. There is a small risk of reversion to virulence, this risk is smaller in vaccines with deletions. Attenuated vaccines also cannot be used by immunodeficientindividuals. Examples: vaccines against poliomyelitis, mumps, measles, rubella, influenza, yellow fever, chickenpox; combined vaccine MMR (mumps, measles, rubella), MMRV (MMR+chickenpox).

2. Inactivated (killed) vaccine consists of virus particles which are grown in culture and then killed using a method such as heat or formaldehyde. The virus particles are

Specific Prophylaxis of Viral Infections

(continuation)

or formaldehyde. The virus particles are destroyed and cannot replicate, the preparation is absolutely safe, but the virus capsid proteins are immunogenic. Boostershots are required periodically to reinforce the immune response. Examples: vaccines against poliomyelitis, influenza, rabies, spring-summer encephalitis, japanese encephalitis, hepatitis A.

Specific Prophylaxis of Viral Infections

(continuation)

3. Subunit vaccine presents an antigen to the immune system without introducing viral particles, whole or otherwise. Theproduction of vaccine involves isolation of a production of vaccine involves isolation of a specific protein from a virus. Such vaccines often elicit weaker antibody responses than the other classes of vaccines. Examples: subunit vaccines against influenza (containing hemagglutinin and neuraminidase).

Specific Prophylaxis of Viral Infections

(continuation)4. Genetic engineering vaccines.Virus-like particlevaccines consist of viral protein(s) derived from the structural proteins of a virus. The highly immunogenicsurface proteins are produced in recombinant Saccharomyces cerevisiae. These proteins can self-assemble into particles that resemble the virus from assemble into particles that resemble the virus from which they were derived but lack viral nucleic acid, meaning that they are not infectious. Because of their highly repetitive, multivalent structure, virus-like particles are typically more immunogenic than subunit vaccines. Examples: vaccines against human papillomavirus (Gardasil) and hepatitis B.

Other vaccine strategies are under experimental investigation. These include hybrid multiply vaccine, DNA-vaccines, peptide epitope vaccines, anti-idiotype vaccines, etc.

How to How to ProduceProduce Viral VaccineViral Vaccine??

virus(production

seed)

Cell culture Harvest Bulk Purification

Inoculation

cell

centrifugation

filtering

How to ProduceHow to Produce Viral Vaccine?Viral Vaccine?(in cell culture)(in cell culture)

Cell culture Harvest Bulk Purification

FormulationFillingLabelingPackaging

Add

Inoculation

Adjuvant Stabilizer

Bulking agent

Preservative

Inspection

How to ProduceHow to Produce Viral Vaccine?Viral Vaccine?(in (in EmbryonatedEmbryonated Eggs)Eggs)

After incubation the egg white contains millions of vaccine viruses which are harvested and then separated from the egg white.

The vaccine virus is injected into a 9 to 12 day old fertilized egg and incubated for 2 to 3 days.(during this time the virus multiplies)