Selection at the haploid and diploid phases: cyclical variation

This paper considers a deterministic model, where selection acts at both the diploid and haploid phases of development. The stability criteria for the maintenance of a protected polymorphism are derived. The implications of the model are examined through several examples, with emphasis on the comparison of these conditions to those of models that view selection as acting only at the diploid or haploid phases. It is found that the consideration of both phases broadens the conditions over such models.

Changes in the virulence of Mycobacterium avium after passage through embryonated hens' eggs

Eight-day-old embryonated hen's eggs were used as a model to study Mycobacterium avium virulence. Strains isolated from human patients caused 20-90% mortality when eggs were infected by injection of bacterial suspensions into the amniotic sac. Virulence of examined strains subsequently decreased with passage through eggs to between 0 and 40% mortality in four passages. Virulence of the egg-attenuated strains could be restored by passage through human peripheral blood mononuclear cells. The site of infection in the egg was usually the mesodermal layer of the chorioallantoic membrane. A few small granulomas containing acid-fast bacteria were seen in the liver, but not in other organs. Death of chicken embryos may have resulted from destruction of the mesodermal layer of the chorioallantoic membrane with consequent respiratory failure. PBMCs infected with less virulent egg-passaged strains of M. avium produced higher levels of tumor necrosis factor-alpha than did peripheral blood mononuclear cells infected with more virulent nonpassaged strains.

Adenovirus masquerading as microsporidia

Enterocytozoon bieneusi is a microsporidian that causes a severe, debilitating, chronic diarrhea in some patients with the acquired immunodeficiency syndrome. Specific diagnosis of E. bieneusi currently requires an invasive biopsy procedure and time-consuming preparation of specimens for electron microscopy. Our attempts to establish an in vitro culture system using mammalian cell cultures inoculated with duodenal aspirates, biopsy, or both, from 2 infected patients resulted in inadvertent coculture of an adenovirus and E. bieneusi. The adenovirus-infected cells deceptively appeared to contain spores of microsporidia based on light microscopic examination. Transmission electron microscopy revealed only a few microsporidia, but numerous cells infected with an adenovirus that was subsequently identified as adenovirus type 8. We believe that adenovirus infections prevented the cultured cells from supporting the proliferation of E. bieneusi and ultimately destroyed the cell cultures.

Evaluation of the chick embryo for the determination of relative virulence of Neisseria meningitidis

The chick embryo model was evaluated as a method to compare virulence between selected strains of Neisseria meningitidis. Inoculation of 13-day-chick embryos via the egg yolk distinguished strains having an LD50 of 10(3) colony forming units (CFU) or greater (low virulence) from those having an LD50 of approximately 10(1) or less (high virulence). A strain of serogroup B and a spontaneous nonpiliated strain of group C were found to be of relatively high virulence while a strain of N. lactamica, a serogroup A carrier strain, and certain nongroupable strains were found to be of low virulence. Strains having an LD50 of 10(2) were not differentiated from either of these. Alternatively, inoculation of the chorioallantoic membrane (CAM) of 9-day-old chick embryos statistically differentiated most strains of N. meningitidis although inoculation via this route was less sensitive.

A tissue culture bilayer model to study the passage of Neisseria meningitidis

A tissue culture bilayer system has been developed as a model to study the mechanisms of attachment and invasion involved in the pathogenesis of Neisseria meningitidis. The model incorporates epithelial and endothelial cell layers separated by a microporous membrane and makes it possible to observe and quantify the passage of bacteria through the multiple layers and to study the mechanisms by which they make this passage. This model is adaptable to a wide variety of microbial pathogens and can be modified by substituting any physiologically relevant eucaryotic cells for the component layers. The system's makeup of cells of human origin and its reproducibility give it advantages over animal and primary organ culture models, while the added complexity of multiple layers allowing cell-to-cell communication makes it a more realistic human tissue model than standard cell monolayers.

Staining qualities of cytomegalovirus inclusions in the lungs of patients with the acquired immunodeficiency syndrome: a potential source of diagnostic misinterpretation

Gomori's methenamine silver and the periodic acid--Schiff reaction stain cytoplasmic but not intranuclear cytomegalovirus inclusions. The biochemical basis of these staining qualities is discussed, and the staining characteristics are correlated with supporting ultrastructural observations. Failure to recognize this phenomenon may lead to erroneous diagnostic conclusions at the light microscopic level.

Virologic studies of HTLV-III/LAV in pregnancy: case report of a woman with AIDS

The number of cases of acquired immunodeficiency syndrome (AIDS) in women is increasing. As of December 30, 1985, 1075 cases in women had been reported to the Centers for Disease Control; 81% of these cases occurred in women of childbearing age (15 to 45 years). The human T-lymphotropic virus type III/lymphadenopathy-associated virus (HTLV-III/LAV) can be transmitted from mothers to their infants. Described is a woman with transfusion-acquired AIDS who was six weeks' pregnant at the time Pneumocystis carinii pneumonia was diagnosed. Despite the fact that HTLV III/LAV was isolated from her peripheral lymphocytes throughout pregnancy, transmission of the virus to her infant or husband does not appear to have occurred.

Primary lymph node pathology in AIDS and AIDS-related lymphadenopathy

Lymph nodes of patients symptomatically infected with the acquired immunodeficiency syndrome (AIDS) virus show a spectrum of morphologic changes ranging from marked lymphoid hyperplasia to marked lymphocytic depletion. These changes can be grouped into three distinct patterns. The type I pattern features follicular and paracortical hyperplasia, and is associated with chronic lymphadenopathy. The type II pattern, which shows diffuse lymphoid hyperplasia but loss of germinal centers, signifies evolution of chronic lymphadenopathy to AIDS. The type III pattern shows marked lymphocytic depletion and represents the end-stage lymph node seen in fatal AIDS. These histologic patterns are closely correlated with the clinical and immunologic status of patients infected with the AIDS virus.

Lymphocyte subsets in lymph nodes of homosexual men with generalized unexplained lymphadenopathy. Correlation with morphology and blood changes

Frozen sections of lymph nodes from 20 homosexual men with chronic generalized lymphadenopathy and of lymph nodes showing follicular hyperplasia from 14 patients without known risk factors of the acquired immunodeficiency syndrome were studied with monoclonal antibodies to T-cell subsets and to the HLA-DR antigen. In T-cell areas of the lymph nodes, excluding tertiary paracortical nodules, the mean T-helper-to-T-suppressor ratio (Th/Ts) +/- 1 SEM was significantly lower in the homosexual group (1.07 +/- 0.06) when compared with the control group (2.49 +/- 0.23), P less than .0001. In seven homosexual men, cell suspensions from the same lymph nodes were analyzed using a fluorescence-activated cell sorter. Results obtained by this method and by immunohistochemistry were comparable except in a homosexual man whose lymph node contained large tertiary paracortical nodules. Although the Th/Ts ratios of the blood and lymph nodes of the same patients were both low, there was not good correlation between the two sets of values (r = .2). Furthermore, there was not good correlation between blood lymphocyte count and lymph node Th/Ts ratios (r = .45). The lymph node Th/Ts ratios of the homosexual patients show less variations compared with the control group. The patient who subsequently developed multiple opportunistic infections had the lowest value. Whether the lymph node Th/Ts ratio has prognostic significance in patients with the lymphadenopathy syndrome warrants further investigation.

Comparison of Legionella pneumophila, L. micdadei, L. bozemanii, and L. dumoffii by transmission electron microscopy

Clinical isolates of Legionella pneumophila, L. micdadei, L. bozemanii, and L. dumoffii were grown on charcoal-yeast extract agar from a living-medium inoculum and prepared for transmission electron microscopy by three different methods. Cells of all four Legionella species possessed cytoplasmic vacuoles, a gram-negative type of cell envelope with a dense peptidoglycan-like layer, a ruthenium red-positive polysaccharide capsule, and a single subpolar flagellum. The dense polysaccharide capsule seen on cells of L. micdadei was separated from the outer membrane by an extra layer of electron-lucent material that was not present on cells of the other species examined.

Value of lymph node biopsy in unexplained lymphadenopathy in homosexual men

The acquired immune deficiency syndrome (AIDS) manifested by severe opportunistic infections, Kaposi's sarcoma, or lymphoma often has a prodrome of lymphadenopathy accompanied by constitutional symptoms. We studied the histopathologic findings of lymph node biopsy specimens and peripheral blood immunologic parameters of 24 clinically indistinguishable homosexual men with chronic generalized lymphadenopathy. Two different morphological patterns were observed: (1) lymph nodes with follicular and paracortical hyperplasia in 21 patients who had had no clinical deterioration and (2) an atypical pattern of lymphoid proliferation in three patients who experienced rapid development of non-Hodgkin's lymphoma and/or opportunistic infections. Several immunologic laboratory results paralleled these changes. Lymph node morphological findings seem to be a useful predictor of outcome in homosexual men with generalized lymphadenopathy.

Pseudogranuloma inguinale caused by haemophilus ducreyi

We used a new selective culture medium to isolate Haemophilus ducreyi from a penile ulcer that had the clinical appearance of granuloma inguinale. The isolation of the organism in pure culture permitted us to make a definitive diagnosis and obtain antimicrobial susceptibility data in a relatively short period. As a result, we were able to change therapy from sulfamethoxazole to erythromycin, and the infection rapidly healed.

Fluorescent-antibody detection of Legionella dumoffii in a fatal case of pneumonia

Legionella dumoffii organisms were detected in the lung tissue from a patient with a fatal case of pneumonia, the second reported to date. A fluorescent-antibody conjugate specific for the Tex-KL organism isolated in 1979 revealed many L, dumoffii organisms in lung tissue obtained postmortem from this patient.

Intracellular multiplication of Legionella pneumophila in cultured human embryonic lung fibroblasts

Cell cultures of normal human embryonic lung fibroblasts were inoculated with two strains of Legionella pneumophila, the etiological agent of Legionnaires disease. Large numbers of intact organisms, including many dividing forms, were seen within fibroblasts by light and electron microscopy. Intracellular multiplication of organisms was demonstrated by the progressive increase in bacterial colony counts from plated extracts of infected fibroblast cultures in which extracellular multiplication had been eliminated by bactericidal concentrations of antibiotics. It is evident that L. pneumophila can thrive in an intracellular environment, and this property may be significant in the pathogenesis of Legionnaires disease.

Pathologic findings in guinea pigs inoculated intraperitoneally with the Legionnaires' disease bacterium

Tissues from guinea pigs inoculated intraperitoneally with the Legionnaires' disease (LD) bacterium were studied with light, immunofluorescent, and electron microscopy. The principal gross lesion was diffuse peritonitis of varying severity. Microscopically, the peritonitis of covered by a mixed inflammatory infiltrate of macrophages, neutrophils, fibrin, and cellular debris. Foci of inflammation and necrosis were consistently observed in the splenic parenchyma, and similar lesions were often found in the lungs, liver, lymph nodes, pancreas, heart, and other organs. Numerous LD bacteria were seen in the peritoneal exudate; fewer were found in disseminated lesions. In electron micrographs, the highest concentrations were seen in macrophages, with fewer organisms present in neutrophils or extracellular spaces. Although the lung is the primary organ konwn to be affected by Legionnaires' disease in humans, our findings indicate that the LD bacterium is capable of dissemination.

Experimental infection of mouse peritoneal mesothelium with scrub typhus rickettsiae: an ultrastructural study

The infection cycle of Rickettsia tsutsugamushi in mouse peritoneal mesothelial cells, observed late in the course of an established infection, intimately involved the host cell plasma membrane. Organisms multiplied in the cytoplasm, moved to the cell periphery, and acquired a host-membrane coat as they budded from the cell surface. Rickettsiae enveloped by this membrane entered other mesothelial cells, apparently by a phagocytic mechanism. Organisms escaped from the phagocytic vacuole as the vacuole membrane and host membrane coat disintegrated. Free rickettsiae replicated by binary fission in the cell cytoplasm. Rickettsial infection of mesothelial cells induced conspicuous cellular hypertrophy with increased numbers of unaltered cytoplasmic organelles.