 Therefore, with this decrease in the number of T cells, the T cells cannot interact and activate the B cells.Normally when B cells are activated they divide, proliferate and differentiate, which includes the differentiation of these cells into plasma cells which are responsible for producing antibodies.However, when there is a deficiency in MHC class II molecules B cells are not activated and cannot differentiate into plasma cells which causes them to be deficient in antibodies which are unable to perform as they are expected.