Superantigens: biology, immunology, and potential role in disease

Cocaine facilitation of cryptosporidiosis by murine AIDS in male and female C57/BL/6 mice

As cocaine may affect progression of the Human Immunodeficiency Virus (HIV) infection to Acquired Immune Deficiency Syndrome (AIDS), we used a murine model of AIDS (MAIDS) induced by LP-BM5 murine leukemia virus to examine cocaine's possible role as a cofactor for secondary parasitic infections. Dissimilarities between the sexes were observed both in the absence and presence of the cocaine. The retrovirus-infected female mice had a much higher rate of Cryptosporidiosis than the retrovirus-infected male mice. Female, but not male, retrovirus-infected mice showed approximately 20-fold more Cryptosporidium per villus section than controls. Compared to respective gender controls, male and female animals infected with the retrovirus infection manifested a heightened Cryptosporidium oocysts count regardless of cocaine treatment. Overall, female groups incurred a higher incidence of infection compared to respective male groups. To determine the role of cocaine, groups of male and female C57BL-6 mice of similar age were treated with cocaine for 4 weeks followed by termination. Cocaine synergized with retrovirus infection in female mice to cause a 30-fold increase in the number of oocyst present. The spleen size and weight of female mice was significantly greater than uninfected controls or male mice. However, due to the very slow progression to murine AIDS in the males, parasite resistance was retained, including in cocaine treated C57BL-6 mice. Thymus cell number in the retrovirus-infected female mice decreased significantly in comparison to uninfected female controls. Continued resistance to the parasite in male mice and its loss in female mice was due to the rate of immunosuppression and thus development of retrovirus-induced murine AIDS.

Superantigens and their potential role in human disease

In the past few years, there has been a virtual explosion of information on the viral and bacterial molecules now known as superantigens. Some structures have been defined and the mechanism by which they interact with MHC class II and the V beta region of the T cell receptor is being clarified. Data are accumulating regarding the importance of virally encoded superantigens in infectivity, viral replication, and the life cycle of the virus. In the case of MMTV, evidence also suggests that superantigens encoded by a provirus may be maintained by the host to protect against future exogenous MMTV infection. Experiments in animals have also begun to elucidate the dramatic and variable effects of superantigens on responding T cells and other immune processes. Finally, the role of superantigens in certain human diseases such as toxic shock syndrome, some autoimmune diseases like Kawasaki syndrome, and perhaps some immunodeficiency disease such as that secondary to HIV infection is being addressed and mechanisms are being defined. Still, numerous important questions remain. For example, it is not clear how superantigens with such different structures, for example, SEB, TSST-1, and MMTV vSAG, can interact with MHC and a similar region of the TCR in such basically similar ways. It remains to be determined whether there are human equivalents of the endogenous murine MMTV superantigens. The functional role of bacterial superantigens also remains to be explained. Serious infection and serious consequences from toxin-producing bacteria are relatively rare events, and it is questionable whether such events are involved in the selection pressure to maintain production of a functional superantigen. Hypotheses to explain these molecules, which can differ greatly in structure, include T cell stimulation-mediated suppression of host responses or enhancement of environments for bacterial growth and replication, but substantiating data for these ideas are mostly absent. It also seems likely that only the tip of the iceberg has been uncovered in terms of the role of superantigens in human disease. Unlike toxic shock syndrome, other associations, especially with viral superantigens, may be quite subtle and defined only after considerable effort. The definition of these molecules and mechanisms of disease may result in new therapeutic strategies. Finally, it is apparent that superantigens have dramatic effects on the immune system. One wonders whether these molecules or modifications of them can be used as specific modulators of the immune system to treat disease.

Genetic and immunological mechanisms in the pathogenesis of systemic lupus erythematosus

Recent research in systemic lupus erythematosus and animal models of lupus has provided new insight into the pathogenesis of this complex autoimmune disease. Progress has been made towards understanding the genetic contributions to disease susceptibility and induction, as well as towards elucidation of the lymphocyte abnormalities involved in pathogenic autoantibody production.