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Infect. Immun., Jan 1998, 305-314, Vol 66, No. 1
R Hanano, K Reifenberg and SH Kaufmann
CD4+ T cells are pivotal for elimination of Pneumocystis carinii from
infected lungs, and alveolar macrophages are considered the main effector
cells clearing the infected host of P. carinii organisms. To investigate
this issue, several mutant mouse strains were used in a previously
established experimental setup which facilitates natural acquisition of
disease through inhalation of airborne fungal organisms. Mutant mice
deficient in major histocompatibility complex class II molecules (A
beta(-/-)), T-cell receptor alphabeta cells (TCR beta(-/- )), or all mature
T and B lymphocytes (RAG-1(-/-)) were naturally susceptible to P. carinii,
whereas mouse mutants lacking the gamma interferon (IFN-gamma) receptor
(IFN-gamma-R(-/-)) or tumor necrosis factor alpha (TNF-alpha) type I
receptor (p55) (TNF-alpha-RI(-/-)) resisted disease acquisition. Analysis
of pulmonary cytokine patterns and free radical expression revealed the
presence of superoxide, nitric oxide, and interleukin-1 (IL-1) mRNA and
elevated levels of IFN-gamma, TNF-alpha, and IL-12 in diseased TCR
beta(-/-) and RAG-1(-/-) mice. Pulmonary macrophages of all diseased mouse
mutants expressed scavenger and mannose receptors. Morbid A beta(-/-)
mutants displayed significant NO levels and IL-1 mRNA only, whereas
heterozygous controls did not exhibit any signs of disease. Interestingly,
neither IFN-gamma nor TNF- alpha appeared to be essential for resisting
natural infection with P. carinii, nor were these cytokines sufficient for
mediating resistance during established disease in the absence of CD4+ T
lymphocytes. Taken together, the results indicated that an activated
phagocyte system, as evidenced by cytokine and NO secretion, in diseased
mutants was apparently operative but did not suffice for parasite clearance
in the absence of CD4+ TCR alphabeta cells. Therefore, additional pathways,
possibly involving interactions of inflammatory cytokines with CD4+ T
lymphocytes, must contribute to successful resistance against P. carinii.
Copyright © 1998, American Society for Microbiology
Activated pulmonary macrophages are insufficient for resistance against Pneumocystis carinii
Department of Immunology, University of Ulm, Germany.
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