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A strain of Legionella longbeachae (Tucker 1) that was isolated from the postmortem lung tissue of a pneumonia patient was serologically distinct from four other strains of L. longbeachae. The recognition of a second serogroup of L. longbeachae represents the first reported instance of serogroup diversity within a species of Legionella other than L. pneumophila. The disease caused by the Tucker 1 strain does not seem to be readily distinguishable from that of pneumonia caused by other legionellae.

The "Pittsburgh pneumonia agent," isolated by Pasculle and co-workers from human lung tissue, has been cultured on artificial media and characterized. The "Pittsburgh" bacterium and the TATLOCK and HEBA bacteria have identical cultural, biochemical, and antigenic characteristics. They also have the same cellular fatty-acid composition, and DNA relatedness indicates that they belong to the same species.

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Several studies ( 1,2,3) have suggested that lethality in acute lymphocytic choriomeningitis (LCM) virus infection of mice is a result of host immunologic response, rather than a direct effect of virus multiplication. Mice inoculated neonatally are protected from lethal effects of the virus, while adult morbidity and mortality can be reduced or delayed by various immunosuppressive methods, including X-irradiation, antimetabolite therapy, and neonatal thymectomy ( 1,2). In the present study, the role of cellular immunity in LCM palthogenesis was further examined, using rablbi t anti-mouse thymo-cyte (RAMT) serum to inhibit host response.Materials and methods. Three-to fourweek-old ICR mice of both sexes were used in all experiments. RAMT serum was prepared as described previously (4), by immunizing rabbits over a several-week period with dispersed suspensions of viable mouse thymus cells. Serum effectiveness was assayed by its ability to (a) diminish peripheral blood lymphocyte counts by 50% within a 4-hour period, and to (b) double the mean survival time of AKR skin grafts on C3H mice. All RAMT sera were shown to be free of anti-LCM activity as assayed by mouse neuat RYERSON UNIV on June 18, 2015 ebm.sagepub.com Downloaded from

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Delayed hypersensitivity in Macaca mulatta infected with either Schistosoma mansoni or mycobacteria was demonstrated by biopsies of skin test sites. Both dialyzable and nondialyzable leukocyte extracts from infected donors transferred delayed hypersensitivity to recipient monkeys. In two recipients, skin test conversion was associated with in vitro transformation of the recipients' lymphocytes.

This report confirms the gram-negative ultrastructural characteristics of the Legionnaires' disease organism by direct examination of pulmonary tissue from six confirmed cases--two from the original Philadelphia epidemic of 1976 and four from more recent sporadic cases. All microorganisms seen in all six lungs were identical ultrastructurally and were predominantely within intra-alveolar macrophages, as previously observed by light microscopy. They appeared as short, blunt rods that were clearly prokaryotic; i.e., they had diffuse electron-lucent nucleoid areas interspersed among areas of well-defined ribosomes, a pinching nonseptic division, and enclosure within a double envelope consisting of two three-layer "unit" membranes, each approximately 75 A wide. This structure, together with a pinching division, is typical of gram-negative bacteria. The Legionnaires' disease organism multiples both intracellularly and extracellularly in tissue and has no unique ultrastructural features that would aid in its specific identification. These findings are compared with recent reports describing the ultrastructure of what was considered to be the Legionnaires' disease organism in yolk sac and culture medium, and in one human lung.