D. Goldman et al., EXPRESSION OF INDUCIBLE NITRIC-OXIDE SYNTHASE IN RAT PULMONARY CRYPTOCOCCUS-NEOFORMANS GRANULOMAS, The American journal of pathology, 148(4), 1996, pp. 1275-1282
Rats, like humans, have extremely effective immune mechanisms for cont
rolling pulmonary Cryptococcus neoformans infection. Tbe mechanism(s)
responsible for efficient immunity in rat experimental infection is un
known. Recently, induction of inducible nitric oxide synthase (iNOS) a
nd nitric oxide (NO) have been implicated as an important microbicidal
mechanism by which activated macrophages effect cytotoxicity against
microbes In this report, we investigated the expression of iNOS in rat
pulmonary cryptococcosis. Localization and regulation of NO productio
n was studied by immunohistochemistry for iNOS in conjunction with imm
unohistochemistry for cell markers, cytokines, and cryptococcal capsul
ar polysaccharide. iNOS immunoreactivity was detected in macrophages,
neutrophils, vascular endothelium, and respiratory epithelium. Double-
immunolabeling studies revealed that the most prominent iNOS immunorea
ctivity was localized to epithelioid macrophages (CD11b/c(+)) within g
ranulomas; CD4(+) and CD8(+) T cells were numerous around granulomas b
ut did not express iNOS. iNOS immunoreactivity was detected itt a sele
ctive population of epithelioid macrophages within some granulomas but
not others. iNOS(-) granulomas were identical to iNOS(+) granulomas w
ith respect to morphology and immunohistochemical profiles Macrophage
iNOS immunoreactivity was detected I weeks after infection ia one out
of four rats and was strongly expressed in all mts at 2 weeks (in up t
o 50% of the granulomas) but declined consider ably by 25 days. iNOS e
xpression coincided with granuloma formation and preceded a decrease i
n lung fungal burden, suggesting an anticryptococcal role for NO. By d
ouble labeling, cytokines that have been shown to promote (interferon-
gamma, granulocyte/macrophage colony-stimulating factor) and inhibit (
transforming growth factor-beta) macrophage iNOS expression were detec
ted around iNOS(+) granulomas. iNOS immunoreactivity was expressed in
selected neutrophils CI and 2 week's) and endothelial cells (1 and 2 w
eeks and 25 days) in the inflamed lung. Airway iNOS immunoreactivity w
as limited to the luminal border of rare bronchiolar epithelial cells
iNOS immunoreactivity was not detected in uninfected rats. The present
study provides the first evidence for association of iNOS expression
with protective cellular responses to cryptococcal infection in vivo.