Moderately virulent strains of Cryptococcus neoformans, inoculated via the trachea, cause a pulmonary infection in BALB/c mice that was gradually resolved by T lymphocyte-dependent mechanisms. The current studies, using monoclonal antibodies to deplete T cell subsets, demonstrated that CD4+ and CD8+ T cells combined to mediate a prominent pulmonary inflammatory infiltrate that included lymphocytes, macrophages, neutrophils, and eosinophils. The inflammatory response peaked 2 weeks after infection and coincided with the beginning of gradual pulmonary clearance of the infection. CD4/CD8 double deficiency (4-8-) markedly reduced the influx of all cells into the lungs. A CD4 deficiency had a more profound effect on the total number of inflammatory cells recruited to the lungs than a CD8 deficiency. Depletion of either CD8+ or CD4+ T cells significantly decreased pulmonary macrophages and neutrophils, but only a CD4 deficiency prevented the influx of eosinophils. Recruitment of CD8+ T cells occurred independently of CD4+ T cells, but CD4+ T cell recruitment to the lungs was significantly reduced in CD8-deficient mice. Mitogen-stimulated infiltrating lung lymphocytes from infected 4+8+ mice secreted both T helper cell type 1 (Th1) [interferon-gamma (IFN-gamma) and interleukin-2 (IL-2)] and Th2 (IL-4, IL-5, and IL-10) cytokines. CD4 deficiency resulted in loss of T cells secreting IL-4, IL-5, and IL-10. However, residual CD8+ T cells still secreted IL-2 and IFN-gamma. Lung T cells from CD8-deficient mice secreted similar levels of IL-4, IL-5, and IL-10 on a per lung basis compared with 4+8+ mice despite decreased numbers of CD4+ T cells, but secreted reduced levels of IFN-gamma. These experiments indicate that (1) CD4+ T cells play a dominant role in recruiting macrophages and granulocytes to the lung and (2) CD8+ T cells also mediate cellular recruitment, increase the magnitude of CD4+ T cell numbers in the infiltrate, and contribute to the local secretion of IFN-gamma. Thus, these studies demonstrate that CD8+ T cells can independently mediate an inflammatory response to a large, particulate, extracellular antigen, a role heretofore attributed almost solely to CD4+ T cells.

A murine model was used to assess the role of cytokines in initiating protective T-cell-mediated immunity in the lung. A pulmonary infection was initiated by intratracheal inoculation of Cryptococcus neoformans (Cne). Previously, we had established that Cne lung clearance was mouse-strain-specific: C.B-17 mice were resistant and developed a Th1-like response, whereas C57BL/6 mice were susceptible and did not develop a Th1 response. In the present study we showed that monoclonal anti-interferon-gamma (IFN-gamma) and anti-interleukin-12 (IL-12) antibody administration prior to infection of resistant C.B-17 mice inhibited lung clearance of Cne. Cytokine profiles of lung and lung-associated lymph nodes (LALN) from monoclonal antibody (mAb)-treated C.B-17 mice were switched from Th1-like to Th2-like, and mAb-treated C.B-17 mice exhibited lung eosinophilia, which was absent in control C.B-17 mice. Additionally, C.B-17 mice treated with anti-IFN-gamma and anti-IL-12 mAb demonstrated a significantly lower percentage of lung macrophages expressing inducible nitric oxide synthase (iNOS) than did control mice. These studies clearly demonstrate that both IFN-gamma and IL-12 are required for initiation of a Th1 response in resistant C.B-17 mice.

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A murine pulmonary infection model utilizing intratracheal inoculation of Cryptococcus neoformans was used to analyze cytokines produced in response to opportunistic pathogens acquired via the respiratory tract. The specific question asked was whether early cytokine secretion in lung-associated lymph nodes (LALN) would predict whether this organism would be cleared from the lung. Lung colony-forming units (CFU) were analyzed in two strains of mice over 12 wk, and lung clearance was found to be strain dependent. C.B-17 mice reduced their lung CFU burden between day 7 and day 14 of infection, had significantly higher in lung CFU than C.B-17 mice. The capacity of cells from lungs and LALN to secrete cytokines was significantly different between the strains when assessed at day 7 and day 14 after inoculation. When compared with sensitive C57BL/6 mice 7 days after infection, resistant C.B-17 mice demonstrated (1) increased interferon-gamma secretion by LALN cells in vitro in response to media alone, heat-killed cryptococci, and the T cell mitogen concanavalin A and (2) increased interleukin (IL)-2 secretion by both LALN and lung cells in response to concanavalin A. IL-4 and IL-10 were comparable or undetectable in both mouse strains, whereas IL-5 was significantly higher in all lung cell cultures of C57BL/6 mice. Thus, an early regional Th1 immune response in C.B-17 mice correlated with resistance to the organism, whereas the absence of this response in C57BL/6 mice correlated with susceptibility.