b cell immunity

IMMUNITY

• The capability to resist any organism or toxin that tend to damage the tissues and organs.

Immunity

Innate = ability to resist damaging organisms and toxinsskin, gastric acids, tissue neutrophils and macrophages, complement, NK cells

Acquired = specifichumoral ----> circulating antibodies(B-cell) cellular ----> activated cells(T-cell mediated)

Preprocessing of the T and B lymphocytes

• Thymus gland preprocesses the T lymphocytes

• Liver and bone marrow preprocess the B lymphocytes

Lymphoid tissue

• Millions of specific types of lymphocytes are stored in the lymphoid tissue.

• All the different lymphocytes that are capable of forming one specificity of antibody or T cell are called a ‘clone of lymphocyte’.

Sequence

Dormant lymphocytes

Invasion of body by foreign antigen

Phagocytosis by macrophages

Presentation of antigen to lymphocytes

Antigen

An antigen is a substance that can induce

an immune response when introduced into

an immunocompetent host and that can react

with the antibody produced from that response.

Bone Marrow

Pre-BCell

Pre-TCell T-Cell

T8-supressor

T4-helper

B-Cell Plasma Cell

IgG IgA IgM IgD IgE

Interactions between T- and B-Cells

Humoral immunity and Antibodies

Formation of antibodies by plasma cells

• Dormant B lymphocyte• Exposure to a specific antigen• Macrophage plays role in the activation

process• Helper T cells also contribute in this activation

process

• These B lymphocytes enlarge to form lymphoblast.

• Further diferentiate into plasmablast• The mature plasma cells(antibody factories)

then produce gamma globulin antibodies.

Formation of Memory cells-difference between primary and

secondary response

virgin cellsfirst exposure to antigen

second exposure to antigen

activated cellsmemory cells

Formation of Activated and Memory Cells

self-antigens

Central lymphoid organ Peripheral lymphoid organ

stimulation

self-antigens

inactivation

Loss of Antigens to Self

Antibodies

antigenbindingsite

hinge region

light chain

heavy chainFab fragment

Fc fragment

IgA, IgD, IgE, IgG, IgM

IgM Antibody

Antibodies• IgG

- 80% total, cross placenta, opsonization

• IgM- first produced, 10-15% total, activate complement

• IgD- not known, may help CD4 Th

• IgA- body fluid, tears, bronchiole secretions, saliva

• IgE- allergic reactions, histamine release

Mechanism of action of antibodies

Direct Action Complement System

Direct action of antibodies on invading agents

1. AGGLUTINATION2. PRECIPITATION3. NEUTRALIZATION4. LYSIS

Complement System

Series of ~ 20 proteinsActivated by microorganismsWill coat the microorganismsPresent normally among plasma proteins

The enzyme precursors can be activated by the

so called ‘classical pathway’

complement

bacteria phagocyte bacteria

2. chemotaxis1. lysis 3. opsonization

Functions of Complement Activation

Antibody-Activated Phagocytosis

Fc receptorbacterium

opsonization

IgE and Histamine Release

IgE receptor

histaminevesicles

binding of IgEto Fc receptor

antigenantigen

release of histamine

binding of antigen

Thank You

T-cells

Act over a short range

Interact with another cell in bodyCan kill or signal other cell

Only recognize antigen when presentedon surface of target cell

T-cells

Cytotoxic Cellskill infected cells

Helper Cells (two types)activate macrophages and B-cells

Suppressor Cellsregulate activity

TH1 TH2

TC LGL

Antibody Production

Virally infected cell andsome tumor cells

Antigenpresentation

activation activation cytotoxicity

macrophage

T-Cell Function

Mhc-molecules

MHC-I present foreign peptides to cytotoxic cells

MHC-IIpresent foreign peptides to helper cells

CYTOTOXIC T-CELLS HELPER T-CELLS

Class IMHC

Class IIMHC

foreignprotein

infectedtargetcell

antigen-presentingcell

Mhc-molecules

Helper T-cells

Helper T-Cells recognize foreign antigen bound toMHC-II proteins on surface of antigen-presenting cells

Helper T-Cells stimulate macrophages and B-cells

Two signals are required for activation of Helper T-Cells

Activation of Helper T-cells

signal 1

signal 2

activation

signal 2 is chemical (interleukin-1) or membrane bound molecule

antigen

Activation of Helper T-cells

signal 1

signal 2

Il-2 receptor

proliferation

Cytotoxic T-cells

Cytotoxic T-Cells recognize viral protein fragments onsurface of infected cells.

Cytotoxic T-Cells induce infected cells to kill themselvesBind to infected cellsInduce cell deathPunch holes in cell membrane

Cytotoxic T-cells

Class IMHC

infectedtargetcell

Perforin discharge

Natural Killer

• destroy virus-infected cells• do not express antigen specific receptors• cells with low levels of MHC I• induce cells to undergo apoptosis

TCRCD8

MHCClass I

Inhibitoryreceptor

Target

No MHCClass I

NK receptor

b cell immunity

infected cells

cells helper

cells

mhc

helper

cell

activation

antibody

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