Question

You are working in a lab that is studying immune responses to highly pathogenic influenza A virus infection. You have isolated antibodies from mice that were given a sub-lethal dose of virus. When these antibodies are intravenously transferred into naive recipient mice, the recipient mice immediately show resistance to what would otherwise be a lethal dose of the virus, and this immunity lasts 1-2 weeks. In experiments to investigate the mechanism underlying this effect, you find to your surprise that the antibodies do not bind to influenza A viral particles. Which of the following is the most likely explanation for the protective effect?

Group of answer choices:

A.The antibodies are specific for secreted viral antigens, and act as opsonins that promote the uptake of these antigens by DCs; this leads to increased presentation of viral peptides on MHC class II molecules, and increased activation of helper T cells

B.The antibodies bind to antigens on the surface of virally-infected cells and trigger cytolysis by NK cells

C.The antibodies are of the IgE isotype and so they bind to IgE receptors on Mast cells and trigger histamine release when damage-associated molecules are released by virally infected cells

D.The antibodies are mainly of the IgM isotype and they activate complement leading to lysis of virally-infected cells

E.The antibodies bind to the CD28 molecule on CTLs and deliver a co-stimulatory signal that enhances killing of cells presenting viral peptides on their MHC class I molecules

Answer 1

answer - option no d is correct which state that the antibodies are mainly of the IgM isotype and they activate complement leading to lysis of virally-infected cell.

reason - antibodies can activate the complement system, which opsonises and promotes phagocytosis of viruses or it damage the envelope of the virus hence destroy the virus .

this is because other option are contradictory to the condition given in the question hence they cant be the reason for the response.  

while the option d statement set fit in the condition or explains the reason for this response ( the recipient mice immediately show resistance to what would otherwise be a lethal dose of the virus)