The document discusses the characteristics and roles of t dependent and t independent antigens in immunology. It highlights how t dependent antigens require T cells for antibody production and lead to the generation of memory B cells, while t independent antigens can directly stimulate B cells without T cell involvement. Key examples include the effectiveness of polysaccharide vaccines and the mechanisms of antibody generation in response to different types of antigens.

1. T DEPENDENT AND
T INDEPENDENT ANTIGENS
Muthubharathi B C
I M.Sc., Biotechnology
2016501012

2. 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

4. ANTIGEN
Immunogenicity
• Induce the immune response
Antigenicity
• Binding ability of antigen with antibody
or cell surface receptors

5. IMMUNOGENICITY
• B cell + Antigen effector T cell + memory B cell
• T cell + Antigen effector T cell + Memory T cell
Plasma cell
CTLs, TH cells

6. 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

8. • 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

11. T DEPENDENT ANTIGENS
T D antigen B cell antigen receptor peptides
MHC II
T cell

12. T INDEPENDENT ANTIGENS
• Follicle dendritic cells (FDC)
• More IgM production Membrane bound immune
complex of T-D antigen
B cell recptors
B cell

13. EASILY SAY THAT
•The antigen which directly
approaches B cell for antibody
production

15. TYPES
• T-ID type- I Ag
Mitogenic stimuli like LPS, CpG or poly IC and B cell mitogens
Function by nonspecifically or polyclonal activity
Elicit the polyclonal B cell activation via Toll like receptors (recognize microbial
molecules, signal cell to secrete immunostimulatory cytokines)
T-ID type-II Ag
Polysaccharides
Able to activate complements
Lack ability to induce MHC dependent T cells
Flexible, Hydrophilic, Nondegradable
Capable of engaging multiple BCRs

17. 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

18. T-ID TYPE II ANTIGEN
• Do not induce immunological memory
• Antibodies to T-ID developed after the age of 2 years
• Biochemical structure
polymeric protein antigen
trinitrophenyl-ficoll (TNP)
Dinitrophenyl-ficoll (DNP)
Eg., Polysaccharides of bacterial capsule – Streptococcus, Haemophilys,
Neisseria

19. 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)

20. GENERATION OF ANTIBODIES TO T-ID
TYPE II
• Membrane immunoglobulin cross linking by multivalent T-ID II ag
B lymphocytes activation requires cross linking of a minimum of 10-20
membrane immunoglobulin response
Non antigenic specific stimuli
Directly target B cell
Indirect via injection of Cytokines or expression of co-stimulatory
molecules of other cells of immune system or complement compounds

21. T-ID C3b C3b+ T- ID
CD21
B cell

23. 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

24. T DEPENDENT VS T
INDEPENDENT