23.
Determine the correctness or otherwise of the following Assertion (A) and Reason (R).
Assertion: An antigen recognized by one immunoglobulin subtype is not recognized by any other subtype.
Reason: Immunoglobulin subtypes differ from each other both in the variable and in the constant regions.

25.
Which of the following statement(s) is/are CORRECT for antigen activated effector T cells?
P. CD4+ cells make contact with macrophages and stimulate their microbicidal activity.
Q. CD4+ cells make contact with B cells and stimulate them to differentiate into plasma cells.
R. CD8+ cells make contact with B cells and stimulate them to differentiate into plasma cells.
S. CD8+ cells make contact with virus infected cells and kill them.

27.
Dizygotic twins are connected to a single placenta during their embryonic development. These twins

29.
Match the cells in Group I with their corresponding entries in Group II.
Group I Group II
P. Mast cells 1. Activation of the complement pathway
Q. Natural killer cells 2. Expression of CD56
R. Neutrophils 3. Contains azurophilic granules
S. Dendritic cells 4. Defense against helminthic infection
5. Production of antibodies specific to bacteria
6. Contains long membranous projections