IL21 and HIV infectious disease: While some of the LN alterations associated with aging and protracted HIV infection appear irreversible, such as increase collagen deposition affecting cell-to-cell contact needed for proper immune crosstalk (54), IL-21 appears to be an immunomodulator capable of enhancing antibody responses to flu vaccination in aging and HIV/SIV through altering the Tfh, monocyte, and B cell responses.