b cell immunity

Copyright © 2006 by Elsevier, Inc.

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

death

Central lymphoid organ Peripheral lymphoid organ

stimulation

self-antigens

death

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’

s

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

B

Antibody Production

Virally infected cell andsome tumor cells

Antigenpresentation

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

Tc Th

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

Th


signal 1

signal 2

activation

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

CD4

antigen


Activation of Helper T-cells

Th


signal 1

signal 2

Th

Il-2 receptor

Il-2

Th Th

proliferation

CD4


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

Tc

infectedtargetcell

CD8

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


TC

TCRCD8

MHCClass I

Inhibitoryreceptor

NK

Target

No MHCClass I

NK receptor

b cell immunity

Technology

infected cells

cells helper

cells

mhc

helper

cell

activation

antibody