Pneumocystis carinii pneumonia in patients without HIV infection.

Pneumocystis carinii is an important, but sporadic, opportunistic pulmonary pathogen in immunosuppressed HIV seronegative persons. Historically, patients at highest risk for P. carinii pneumonia are included infants with severe malnutrition, children with primary immunodeficiencies, patients with hematological malignancies, and recipients of solid organ or bone marrow transplants. Recently, solid tumor patients, in particular those receiving high-dose corticosteroids for brain neoplasms, and patients with inflammatory or collagen-vascular disorders, especially patients with Wegener granulomatosis receiving immunosuppressive therapy, have been identified as subgroups at increased risk for P. carinii pneumonia. Other factors associated with P. carinii pneumonia include the intensity of the immunosuppressive regimen and tapering doses of corticosteroids. Because P. carinii pneumonia is associated with significant morbidity and mortality, it is important to identify high-risk patient populations to administer effective chemoprophylactic agents, such as trimethoprim-sulfamethoxazole.

Characterization of a multicopy family of genes encoding a surface-expressed serine endoprotease in rat Pneumocystis carinii.

A unique family of genes encoding serine endoproteases related to the Saccharomyces cerevisiae serine endoprotease kexin was identified in Pneumocystis carinii. Unlike previously described serine endoprotease genes that are single copies, multiple copies of the P. carinii serine endoprotease are distributed throughout the genome. The proteins predicted by these variant genes demonstrate sequence variability, but they retain the conserved active sites associated with endoprotease activity. The serine endoprotease was localized to the organism surface by immunohistochemical and immunofluorescence studies and to the electron lucent layer of the cyst wall by immunoelectron microscopy. The findings of multiple copies of the serine endoprotease gene in the P. carinii genome, and its localization to the cell surface, suggest that this protease plays an important role in the biology of P. carinii and that antigenic variation of the surface-expressed serine endoprotease may be a strategy for immune evasion. P. carinii serine endoprotease provides a novel target for chemotherapeutic and immune-based approaches to the treatment of P. carinii pneumonia.

Pneumocystis carinii: a fungus resistant to antifungal therapies - mechanisms of action of antipneumocystis drugs.

Pneumocystis carinii is a pathogen that causes a potentially lethal pneumonia in patients with AIDS and other immunodeficiency states. This review discusses the mechanisms of action of four classes of antipneumocystis agents: inhibitors of ergosterol synthesis and function, 1,3-beta-glucan synthase inhibitors, antifolates and DNA binding agents. Investigations of P. carinii's biologic pathways affected by the antipneumocystis actions of each of these classes of agents has generated important insights into the organism's basic biology and supports the organism's classification as a fungus. In addition, this review discusses some recent P. carinii research and its potential impact on drug development.

Pneumocystis carinii in Africa: an emerging pathogen?

PIP: There are quite a few pathogens which can cause pneumonia. Identifying the agent of infection simplifies therapy by allowing the appropriate treatment to be targeted with a minimum amount of toxic drugs. Empirical therapy is ideally reserved for settings in which the patient is not acutely ill, there is a high probability of a single, easily treated pathogen, and rapid diagnostic facilities are available if treatment fails. Empirical therapy, however, is often necessary in many AIDS-endemic regions where diagnostic tests are unavailable due to limited resources. In such circumstances, a treatment algorithm independent of extensive diagnostic testing and targeted against locally prevalent pathogens is called for. Malin and colleagues have reported finding Pneumocystis carinii pneumonia (PCP) among 33% of 64 patients in Zimbabwe observed with diffuse pneumonia unresponsive to penicillin. Untreated PCP is lethal. Further, despite three negative sputum smears for Mycobacterium tuberculosis, the organism was the most common pathogen ultimately identified, confirming previous reports and highlighting the importance of anti-TB therapy. The high incidence of PCP raises concerns that in certain parts of Africa treatment algorithms which do not consider PCP may need to be re-evaluated. Different patient selection criteria among studies with discordant results may partially explain the differences in the incidence of PCP in different parts of Africa. Otherwise, regional environmental differences, host genetic variation, and differences in the virulence of various strains of P. carinii may play a role. Data on the incidence of PCP in HIV-infected infants in Africa would provide insights into the role of P. carinii as a pathogen. The authors note that if the incidence of PCP is rising, even in selected areas, then prophylaxis in such areas with co-trimoxazole may be a cost-effective management approach which may also decrease the incidence of bacterial infections. Alternatively, early empirical therapy with co-trimoxazole at high doses may be an effective approach for treating both PCP and bacterial infections before the initiation of empirical anti-TB therapy.^ieng

Natural killer cells are deficient in the surface expression of the complement regulatory protein, decay accelerating factor (DAF).

Decay-accelerating factor (DAF) is a 75,000 m.w. membrane protein that inhibits autologous complement C3 activation at the cell surface. One-color direct immunofluorescence with anti-DAF antibody and cytofluorographic analysis indicates that normal human monocytes and granulocytes are uniform in expression of DAF, whereas 23% of peripheral blood lymphocytes are DAF deficient. A two-color indirect immunofluorescence method, used to define the phenotype(s) of the DAF-deficient lymphocytes, was less efficient in DAF detection and led to overestimation of the fraction of deficient cells. Nonetheless, the difference between DAF expression by natural killer cells, identified by the CD16 and HNK-1 antigens, was marked. DAF deficiency was intermediate in cells expressing the CD2, CD3, CD4, or CD8 markers. On the basis of the phenotypic definition of natural killer cells and their contribution to the lymphocyte population, it is concluded that a uniform deficiency of DAF on natural killer cells accounts for about one-half of the DAF-deficient lymphocytes in peripheral blood of normal donors. The finding of a complete DAF deficiency in the lymphocytes from a patient with a lymphoproliferative disorder with the predominant proliferation of CD2+, CD3+, CD8+, HNK-1+ large granular lymphocytes gives additional support for the association of DAF-deficiency with natural killer cells.