Immunohistochemical characterization of human fulminant amoebic colitis.

In cases of fulminant amoebic colitis we have determined the interactions between Entamoeba histolytica trophozoites and immune cells in order to better understand the pathophysiology of amoebic colitis. Eleven specimens of amoebic colitis and five specimens of colon without amoebic lesions were studied. Trophozoites and immune cells were located by topographic stains, histochemistry and immunohistochemistry. Trophozoites were seen in both damaged and undamaged areas of the colonic mucosa. Specimens of fulminant amoebic colitis showed: (a) an increase in IgA+, IgG+ B cells and neutrophils; (b) a reduction in IgM+ B cells, CD8+ T cells, macrophages, eosinophils and mast cells; and (c) no change in the number of NK and CD4+ T cells. The cellular infiltrate in amoebic colitis may represent the combined effects of amoebic monocyte locomotion inhibitory factor and switching of IgM+ B cells to IgG+ and IgA+ plasma cells, induced by amoebic antigens. Tissue damage in the absence of trophozoites may result from ischaemia or host immune responses.

Nocardiasis in patients with HIV infection.

The frequency of Nocardia infection in HIV-infected patients has increased during the past few years from 0.3% in 1985 to 1.8% in 1989. Although it is not of great concern as an AIDS-associated infection, the nonspecific clinical presentation in these patients might be confused with other lung infections such as tuberculosis (TB). The mortality rate can be as high as 60%. The authors diagnosed three homosexual men with nocardiasis among 1060 HIV-infected patients (0.2%) in a tertiary care center in Mexico City from 1981 to 1997. The mean age was 32 years. The CD4 count was less than 260 cells/mm3 in all these individuals. The clinical presentations were subacute sinusitis, chronic localized abdominal abscess, and acute disseminated nocardiasis. The respective associated infections were none; TB and cytomegalovirus (CMV); and candidiasis, TB, CMV, Isospora belli, and disseminated Mycobacterium avium complex (MAC). Trimethoprim/sulfamethoxazole (TMP/SMX) was the treatment in all the cases; at the time of this writing, two patients were living and one had died during the acute episode. A literature search uncovered 130 cases of Nocardia infection in HIV patients since 1982. According to the published data and our results, nocardiasis should be suspected in those HIV-infected patients who (1) do not respond to appropriate antituberculous treatment; (2) are intravenous drug users; and (3) develop a characteristic pericardial infection. Finally, adequate surgical or percutaneous drainage of abscesses are extremely valuable for diagnosis and therapy.