T DEPENDENT AND T INDEPENDENT ANTIGENS

Muthubharathi B CI M.Sc., Biotechnology2016501012

A BRIEF ABOUT ANTIGEN• Ladislas Deutsch, 1899• Induces the production of antibodies• Antibody generator• Can be recognized by antibody when binds with MHC molecules• Soluble compounds

ANTIGEN

Immunogenicity• Induce the immune response

Antigenicity• Binding ability of antigen with

antibody or cell surface receptors

IMMUNOGENICITY• B cell + Antigen effector T cell + memory B cell

• T cell + Antigen effector T cell + Memory T cell

Plasma cell

CTLs, TH cells

T DEPENDENT ANTIGENS• Do not directly activates antibodies• Depends on T cells for the production of cytokines• Cytokines supports the activation, proliferation and

differentiation of B cells• Cytokines helpful for both cell mediated and humoral immune

response

• T-D antigens elicit memory B cells, which develop in T-D germinal

centers

• Can be identified by somatic mutation in their Ig loci or by surface expression of secondary Ig isotypes

T DEPENDENT ANTIGENS

T D antigen B cell antigen receptor peptides

MHC II

T cell

T INDEPENDENT ANTIGENS• Follicle dendritic cells (FDC)• More IgM production Membrane bound immune

complex of T-D antigen

B cell recptors

B cell

EASILY SAY THAT

•The antigen which directly approaches B cell for antibody production

TYPES • T-ID type- I Ag

Mitogenic stimuli like LPS, CpG or poly IC and B cell mitogensFunction by nonspecifically or polyclonal activityElicit the polyclonal B cell activation via Toll like receptors (recognize

microbial molecules, signal cell to secrete immunostimulatory cytokines)

T-ID type-II AgPolysaccharides Able to activate complementsLack ability to induce MHC dependent T cellsFlexible, Hydrophilic, NondegradableCapable of engaging multiple BCRs

RECENT STUDY• T-ID type II antigens elicit robust and long lasting primary

antibody responses in mice but cannot recall response, ie., secondary immunization

• Polysaccharide vaccines – Pneumovax and Menomune confer long term humoral protection in adult humans

• T-ID type II stimulate extrafollicular foci of plasma cell production and short lived abortive T-ID germinal centers

T-ID TYPE II ANTIGEN• Do not induce immunological memory• Antibodies to T-ID developed after the age of 2 years

• Biochemical structurepolymeric protein antigentrinitrophenyl-ficoll (TNP)Dinitrophenyl-ficoll (DNP)

Eg., Polysaccharides of bacterial capsule – Streptococcus, Haemophilys, Neisseria

B CELL OR T INDEPENDENT ANTIGEN

• Bound in narrow grooves or deep pockets of the antibody. Protein B-cell epitopes are much larger and interact with a larger, flatter complementary surface on the antibody molecule.

• But, memory B cells are derived from T-D antigens (Widely accepted)

GENERATION OF ANTIBODIES TO T-ID TYPE II

• Membrane immunoglobulin cross linking by multivalent T-ID II agB lymphocytes activation requires cross linking of a

minimum of 10-20 membrane immunoglobulin response

Non antigenic specific stimuliDirectly target B cellIndirect via injection of Cytokines or expression of co-

stimulatory molecules of other cells of immune system or complement compounds

T-ID C3b C3b+ T- IDCD21

B cell

ROLE OF DENDRITIC CELLS

Dendritic cell

T cell activated T cell cytokines B cell

B cell

Activated B cell

Both T dependent and T independent B lymphocyte activation

T DEPENDENT VS T INDEPENDENT