Martine Y. K. Armstrong

Reduced binding and phagocytosis of Pneumocystis carinii by alveolar macrophages from persons infected with HIV-1 correlates with mannose receptor downregulation.

The macrophage mannose receptor, a pattern recognition molecule and component of innate immunity, mediates binding and phagocytosis of Pneumocystis carinii and likely represents an important clearance mechanism in the lungs of immunocompetent hosts. The purpose of this study was to examine the ability of alveolar macrophages from HIV-infected individuals to bind and phagocytose P. carinii, and to investigate the role of the macrophage mannose receptor in mediating this interaction. Compared with healthy individuals, alveolar macrophage phagocytosis of P. carinii from HIV+ persons was reduced up to 74% (P = 0.02), primarily reflecting a reduction in the number of organisms associated with each macrophage (P = 0.019). Furthermore, macrophages from HIV+ individuals demonstrated up to an 80% (P < 0.05) reduction in mannose receptor surface expression and endocytosis. Mannose receptor affinity was unaltered, and mRNA levels were modestly reduced (P < 0.05). Cells from HIV+ individuals with CD4(+) counts < 200 cells/mm3 (representing individuals at high clinical risk for P. carinii pneumonia) demonstrated the lowest levels of P. carinii phagocytosis and mannose receptor endocytosis. In vitro HIV infection of alveolar macrophages from healthy individuals reduced mannose receptor endocytosis to 53.2% (P < 0.05) and P. carinii binding and phagocytosis to 67.4% (P < 0.05) of control. Our studies suggest that HIV infection may alter innate immunity in the lungs, and that impaired alveolar macrophage mannose receptor-mediated binding and phagocytosis of P. carinii may contribute to the susceptibility of HIV-infected individuals to this opportunistic pulmonary pathogen.

The challenge of Pneumocystis carinii culture.

ABSTRACT. Published and unpublished data on the cultivation of P. carinii were reviewed by a panel of investigators convened by the National Institutes of Health. Although several cell culture systems allow propagation of P. carinii for a limited time with modest rates of replication, these have not proved adequate for isolation of P. carinii in sufficient quantity to explore important basic biological investigation. Attempts at cell‐free culture have yielded only transient proliferation. Because much of the unsuccessful work on cultivation of the organism has been unpublished, the panel agreed that these data may be useful to other investigators in designing experimental strategies for cultivation. Therefore, the purpose of this report is to make available this information to researchers, lest others unknowingly repeat unsuccessful methods. It is hoped that by documenting the history and the complexities of Pneumocystis culture, renewed interest and efforts will be directed toward this fundamental scientific challenge.

Role of endogenous murine leukemia virus in immunologically triggered lymphoreticular tumors II. Isolation of B-tropic mink cell focus-inducing (MCF) murine leukemia virus

Abstract Previous work has shown that (BALB/c x A)F, (CAF 1 ) mice with an immunological disorder, the graft-versus-host reaction (GVHR), express an oncogenic murine leukemia virus (MuLV) which appears to be responsible for the subsequent development of lymphoreticular tumors. A mink cell focus-inducing (MCF) virus has been isolated from a reticulum cell neoplasm induced in a BALB/c mouse by serially passaged B-tropic MuLV originating in a CAF, GVHR mouse. The cloned MCF virus has a dual host range. It grows both in mouse cells where it is XC negative, B tropic, and in mink lung cells where it induces characteristic foci. It is partially neutralized by xenotropic MuLV antiserum and it partially competes in a homologous ecotropic gp70 radioimmunocompetition assay. Both ecotropic and xenotropic MuLV interfere with its infectivity. In these biological properties, the GVHR MCF virus closely resembles recombinant AKR MCF virus. We discuss the possible origin and significance of a presumptive recombinant MuLV in a low virus model where lymphoreticular tumors are triggered by an immunological disturbance.

Propagation and Purification of Rat Pneumocystis carinii in Short‐Term Cell Culture

A short-term cell culture is used to propagate and purify rat-derived Pneumocystis carinii (Pc). An aliquot of pelleted material washed out of the lungs of rats with moderate to severe Pc pneumonia is cultured for 7 to 10 days on the adherent mink lung cell line Mv 1 Lu, and the rest of the material is frozen down in medium with 10% glycerol. Although it has not been established that substantial multiplication of Pc occurs in culture, the Pc organisms harvested from the supernatant at the end of the culture period are relatively free of both host and feeder cells. This is in marked contrast with the lung wash inoculum in which the Pc organisms are heavily contaminated with rat cells and enmeshed in a highly sticky material. Lung wash preparations frozen down in glycerol and stored at -70 degrees C for as long as 6 months or more can be successfully cultured upon thawing with no apparent loss of viability of the Pc organisms.