Bacterial and Fungal Products

There are a number of immunomodulators of bacterial origin, most of which activate lymphocytes in a variety of ways (Table 1). Many bacterial cell surface components activate lymphocytes, but little is known about the ability of bacterial exotoxins to stimulate lymphocytes, probably because the extremely high cytotoxicity of typical exotoxins such as diphtheria make it technically difficult to examine their stimulatory effects on immunologically competent cells, including lymphocytes.