CD4 and HIV infectious disease: In cases such as immunosuppressive therapy or HIV infection, decreases in the CD4+ T cell count can directly contribute to the development of OIs.[34] CD4+ T cells play a central role in modulating host immune responses to pathogens, and along with CD8+ T cells, make up the majority of T lymphocytes.[35] CD4+ T cells carry out multiple functions, including the activation of B-lymphocytes and cytotoxic T cells.[36] These “helper” CD4+ T cells do not neutralize infections but rather trigger the body's response to infections.