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After observations that Macaca nemestrina were exceptionally susceptible to simian immunodeficiency virus and human immunodeficiency virus type-2 (HIV-2), studies of HIV-1 replication were initiated. Several strains of HIV-1, including a recent patient isolate, replicated in vitro in peripheral blood mononuclear cells (PBMCs) and in CD4-positive M. nemestrina lymphocytes in a CD4-dependent fashion. Eight animals were subsequently inoculated with either cell-associated or cell-free suspensions of HIV-1. All animals had HIV-1 isolated by cocultivation, had HIV-1 DNA in their PBMCs as shown by polymerase chain reaction, and experienced sustained seroconversion to a broad spectrum of HIV-1 proteins. Macaca nemestrina is an animal model of HIV-1 infections that provides opportunities for evaluating the pathogenesis of acute HIV-1 replication and candidate vaccines and therapies.

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ABS1RACr Within seconds after exposure of rat peritoneal mast cells to polymyxin B, bulges appear on the surface of the cells. Freeze-fracture electron microscopy reveals that each bulge overlies a mast cell granule. In contrast to the even distribution of intramembranous particles in the plasma membrane of unstimulated cells, the intramembranous particles in the stimulated cells are unevenly distributed in the membrane of the bulges with large patches of membrane lacking intramembranous particles. The membranes over the most prominent bulges are entirely free of intramembranous particles, and in some instances there is an increased concentration of intramembranous particles at the margins of the bulges. Perigranule membranes exhibit the same changes in distribution of intramembranous particles. Electron microscopy of thin sections of rapidly fixed, stimulated mast cells shows a peculiar structure of the membrane overlying some bulges; instead of the pentalaminar membranes previously demonstrated, the membrane at these sites of presumptive fusion of perigranule and plasma membrane assumes the form of a single dense lamina with a fine fuzzy coating on either side. It seems possible that membrane fusion and subsequent pore formation proceed in the stimulated mast cell through a stage of flight of intramembranous particles and molecular rearrangement of the other membrane components.It is well established that specific membrane-bound cytoplasmic granules represent the storage form of histamine and heparin in mast cells (1-3). The granules are extruded from the cell under the influence of a variety of agents. Induced granule secretion has been shown to occur by exocytosis (4), in which apposing membranes of granules and cell surface interact to establish an opening (5). Involvement of membranes surrounding other granules produces a series of channels that penetrate well into the cell domain (6, 7).The extent of membrane interaction occurring during secretion would be expected to make the mast cell a particularly favorable object for the investigation of secretory membrane events. We have previously reported on the appearance of normal unstimulated mast cells with the freeze-fracture technique (8). The application of freeze-fracture technique to the study of mast cell secretion provides information complementary to that available from the previously used modes of morphologic analysis (5). MATERIALS AND METHODSPeritoneal cells, including mast cells, were collected from the peritoneal cavities of 2-to 4-month-old male CDF rats obtained from Charles River Breeding Laboratories Inc., Wilmington, Mass., or bred in our departmental animal facilities from CDF stock. In each of the degranulation experiments performed, six to eight rats were used. Six to ten million mast cells were separated from the other peritoneal cells by centrifugation through 35% albumin (9), so that mast cells constituted at least 80% by number of the final cell suspension. Mast cells were then washed once and suspended in balanced salt solution (9) at...