IMMUNITY TO RHODOCOCCUS-EQUI

Rhodococcal pneumonia is an important, life threatening disease of foa ls and immunosuppressed humans. Increased knowledge of the mechanisms of protective immunity are required in order to develop an effective i mmunoprophylaxis strategy for horses and immunotherapeutic regiments f or people. Both humoral and cellular components of the immune system m ay be involved in immune clearance of R. equi. The susceptibility of f oals less than 4-6 months of age is postulated to reflect waning mater nal antibody, and passive transfer of hyperimmune plasma can provide p rotection on endemic farms. However, effective clearance is likely to require appropriate cellular responses, including the secretion of cyt okines. In murine models, both CD4 + and CD8 + T lymphocytes can reduc e bacterial counts in the lung. CD4 + cells appear to be both required and sufficient, and IFN-gamma is a primary mediator. Clearance appear s to be a type 1 immune response while type 2 responses may lead to a failure to clear and lesion development. It remains to be determined h ow the cellular immunity experiments reported in mice relate to horses and humans. Likewise, the role of specific R. equi antigens in protec tive immunity has not been determined. (C) 1997 Elsevier Science B.V.