Question

A mouse has the following phenotype:

i. It adeptly clears virus infections without issue.
ii. When its B cells are co-cultured in a dish with T cells from a normal mouse, antibodies of all subclasses are produced.
iii. In the serum of the mouse, IgM is abundantly present, but all other subclasses are severely reduced.
iv. Macrophages from the mouse are adept at clearing bacterial infections
v. Production of IL-4, IL-5, and IL-13 by T cells are unhindered

What is the likely cause of this phenotype?

	The mouse does not have CD8+ T cells
	Its T cells do not express CD40L
	Its B cells do not express CD40
	The mouse does not have neutrophils
	The mouse does not have CD4+ T cells

Answer 1

The correct answer is option b- Its T cells do not express CD40L.

Explanation: T cells do not express CD40L, CD40 is a co-stimulatory receptor present on B cells . When it bound to CD40L, it sends signal to B-cell receptor and helps in class switching. So from IgM different other subtypes of antibody (IgG, IgA, IgE) are produced. When CD40L is not present on T-cell surface, proper interaction cannot occur and the class switching from IgM to other subtypes of antibody do not occur. This is called Hyper IgM syndrome. Here when B cells are incubated with ormal T cells from normal mouse, the class switching occurs as normal ouse T cell has te normal CD40L. So it proves that This mouse; T cell lacks CD40L.