Atypical cutaneous leishmaniasis in Central America: possible interaction between infectious and environmental elements.

Biopsies of 71 cases of atypical cutaneous leishmaniasis from Costa Rican patients were evaluated by histopathological procedures and attempts were made to culture Leishmania from nine biopsies. Leishmanin skin tests were carried out in 31 patients and 112 healthy individuals. Additional biopsies from 19 patients from Nicaragua were evaluated by routine histopathology. Ten biopsies were studied by confocal and nine by scanning electron microscopy. Inorganic material was analysed using an electron probe for microanalysis. Leishmania parasites were isolated from only two biopsies, but 90.3% of the patients from Costa Rica were leishmanin-positive, as were 27.7% of healthy individuals. Routine histopathological studies revealed naked granulomas formed by differentiated macrophages. Abundant inorganic material was observed in sections examined by confocal microscopy. Electron probe analysis revealed that silica and aluminium were the predominant elements in large particles. We postulate that the presence of this inorganic material, possibly of volcanic origin, in the skin may modulate the immunological response to Leishmania and may inhibit visceralization in the cases caused by Leishmania chagasi.

Comparative histopathology in BALB/c mice infected with virulent and attenuated strains of Brucella abortus.

The course of infection in BALB/c mice of virulent Brucella abortus strain 2308 (S-2308) and attenuated strain 19 (S-19) varies markedly. Whereas S-19 is eliminated at an exponential rate beginning at 2 weeks post infection (p.i.), strain 2308 assumes a steady state or plateau during the first 6 weeks p.i. and thereafter is eliminated very slowly over a period exceeding 6 months. Here we compared the initiation and maintenance of inflammatory reactions in spleens and livers of mice infected with either of the two strains of B. abortus for the first 6 weeks p.i. Histological changes in the liver were similar in response to either strain and were characterized by the development of small granulomas and an influx of polymorphonuclear leukocytes (PMN) and monocytes. Tissue reactions in the spleen were similar at weeks 1 and 2 p.i. At 3 weeks p.i. and thereafter, focal granulomatous responses in S-2308-infected mice exceeded those in mice infected with S-19. Numbers of nonspecific esterase (NSE) positive mononuclear leukocytes in S-19-infected spleens had increased by 3 weeks p.i. and remained elevated. No comparable increase in NSE positive cells occurred in mice infected with S-2308, and numbers were significantly lower. At 4 weeks p.i. the influx of mature neutrophils and the intensity of extramedullary hematopoiesis were significantly greater in S-19-infected spleens. A profound depletion of periarteriolar lymphoid tissue was noted in both infections for the first 3 weeks p.i. However, repopulation of lymphoid sheaths in S-19-infected spleens became significantly greater by 4 weeks p.i. and continued to increase at significantly higher levels during the next 2 weeks. This study demonstrates quantitative differences in splenic inflammatory responses which are temporally related to the more rapid elimination of S-19. Based upon the lower susceptibility of strain 2308 to the protective effects of immune serum it is hypothesized that the different patterns of infection and inflammation displayed by the 2 strains may related to the differential capacities of antibody opsonized S-19 and S-2308 to survive in activated macrophages.

Comparative protection of mice against virulent and attenuated strains of Brucella abortus by passive transfer of immune T cells or serum.

Passively transferred immune serum provided significantly greater protection to BALB/c mice against attenuated Brucella abortus 19 than against virulent strain 2308, whether serum donors had been infected with strain 19 or 2308. In contrast, immune T cells conferred better protection upon recipients challenged with the homologous strain of B. abortus. It is hypothesized that strain 2308, but not strain 19, can survive in macrophages after opsonization and that epitopes which induce protective cell-mediated immunity may differ between strains 19 and 2308.

Temporal development of protective cell-mediated and humoral immunity in BALB/c mice infected with Brucella abortus.

In BALB/c mice infected i.v. with attenuated strain 19 of Brucella abortus, the organism replicates to high numbers in the spleen and reaches peak concentrations at 2 wk postinfection (p.i.). The infection is then progressively cleared so that by 8 wk p.i. numbers of bacteria have decreased 10,000 fold or more. Passive transfer assays were performed with T cell-enriched spleen cells and serum of donor mice infected 2, 3, 4, 5, 6, or 8 wk previously. Antibodies conferred significant protection to recipients at and after 3 wk p.i., whereas protection by T cells was not evident until 4 wk p.i. The combined transfer of serum and cells enhanced protection over that provided by serum or cells alone when transfers were made before, but not after, challenge infection. Protection conferred by T cell-enriched spleen cells of 6-wk donors was unaffected by the presence of equal quantities of cells from 3-wk donors, but was abrogated by the removal of both CD4 and CD8 T cell subsets. Experiments with purified CD4 and CD8 subsets revealed that cell-mediated protection resided at equivalent levels in both subsets. Daily treatment of mice with Cyclosporin A for 4 wk after infection caused some increase in numbers of brucellae in spleens and livers. Although immune responses of treated animals were markedly suppressed, there was little effect of treatment on numbers of macrophages in the spleen, on enhanced killing of Listeria monocytogenes in the spleen, or on the nature and intensity of splenic and hepatic inflammatory responses. These data indicate that acquired resistance to infection with B. abortus in mice is the result of independent, and probably also interactive, effects of antibodies and T effector cells of both CD4 and CD8 phenotypes. The initial decline in bacterial numbers in the spleen, which occurred in the absence of detectable cell-mediated immunity in that organ, could probably be ascribed principally to effects of antibodies and to nonimmune stimuli responsible for increased formation, attraction, and activation of macrophages.