CD4 and infection: CD3+ and CD4+ lymphocyte subpopulations are important indicators of cellular immune function; CD3+ reflects the overall level of cellular immune function, and its reduced level indicates suppressed cellular immune function; CD4+ plays an important role in recognizing foreign antigens, mediating the production of inflammatory factors and fighting infection, etc. Reduced CD4+ leads to the production of lymphokines and assists B lymphocytes in the production of antibodies, and assists the decreased function of other lymphocytes.