Accompanying their Th2 response is a high level of IL-4 production. Of interest is that IL-12 given to mice susceptible to Leishmania major with soluble Leishmania antigens has resulted in immunoprotection of these mice to subsequent infection with Leishmania major . A clearer understanding of the importance of the Th1 response in defense against Leishmania major infection has evolved from the analysis of the susceptibility of this inbred strain to infection by this intracellular parasite. Additionally, development of strategies for using specific cytokines with antigens to specifically activate T cell clones is likely possible. Studies paralleling the work on this model system of Leishmania infection are already underway for fungal diseases.
Lymphocytes comprise a critical component of host defenses against cryptococcosis.
Freshly isolated T and NK cells are conjugate with, and directly inhibit the growth of Cryptococcus neoformans . During in vitro culture, the fungistatic capacity of human lymphocytes is lost unless the cells are activated with the cytokine interleukin-2. Recent studies have defined the conditions under which human leukocytes produce TNF- , when stimulated by C. neoformans. Fractionation of PBMC established that monocytes were the predominant source of TNF- . However, this decline was reversed if the BAM and monocytes were cultured with interferon g.