Question

1.What best describe a thymus independent type 2 antigen?

a.Can only activate mature B cells.

b.can only activate immature B cells.

c.Babies respond well to these antigens.

d.Induce high affinity antibodies

Answer 1

Ans.

The answer is (a) Can only activate mature B Cells.

Explanation:

The immunogen that can stimulate B cells without the requirement of T Cells,to synthesize antiobdies are called as a Thymus independent antigen or TI antigen. Polysaccharides containing repeating lipopolysaccharides (LPS) that are dervied from gram-negative microorganisms forms these thymus-independent antigens.TI Antigen is classified into two groups:

1. TI-1 Antigen - They are responsible for the activation of intrinsic B Cells with the help of binding of toll like receptors or by extensive BCR crosslinking to repeated epitopes. B cells thus activated proliferate outside the lymphoid follicles.
2. TI-2 Antigen - They consists of repetitive epitopes of bacteria with polysaccharide layer outside the cell envelope.They cannot activate intrinsic B cells,instead can only activate mature B Cells.This is because of extensive surface lg crosslinking by their determinants that triggers signal transduction in B cells.