Peritoneal free cells from 86 adult mice of both sexes were studied quantitatively and qualitatively.Peritoneal free cells were examined by use of a Coulter counter and channelyzer. The size-distribution curves of peritoneal free cells thus obtained show three peaks, which were almost constant in position in all the cases examined. Thus, peritoneal free cells can be classified into three major populations according to cell size. The total cell numbers of the three populations, composed of small, medium-sized and large cells are, on the average, 1.60 x lo6, 2.47 x lo6 and 2.90 x lo6 in males and 2.05 x lo6, 5.57 x lo6 and 3.86 x lo6 in females a t 65 days of age. The number of medium-sized cells is significantly greater in females than in males.Morphologically, three types of peritoneal cells, which constitute the three populations, can be distinguished cytologically and cytochemically, when examined by light microscopy and scanning and transmission electron microscopy. These type I, 11, and 111 cells correspond closely to the three components in the size distribution curves in cell size.Type I cells are small lymphocytes. Type I1 cells are medium-sized, round mononuclear cells which are distinguishable from lymphocytes by their ultrastructural characteristics, and they constitute a major population which can be separated from the other two populations. Type I11 cells are macrophages. In the peripheral cytoplasm, they have a labyrinth of tubules which open on the cell surface.Macrophages have recently attracted much attention in relation to immune response (van Furth, '75; Nelson, '76). The peritoneal cavity is known to contain so many free macrophages that macrophages are generally obtained from the peritoneal cavity for experimental study (Stuart et al., '73). However, the peritoneal cavity contains other kinds of free cells in addition to macrophages (Felix and Dalton, '55; Padawer and Gordon, '56; Bennett, '65; Carr, '67; Davis and McGowan, '68; Gallily and Ben-Ishay, '74; Daems and Koerten, '78). Therefore, exact knowledge of free cells in the peritoneal cavity is needed for studies using peritoneal free cells. However, very little is known about cellular constituents other than macrophages in the peritoneal cavity (Catanzaro and Graham, '74; Gallily and Ben-Ishay, '74). In this study we attempted to examine the peritoneal free cells qualitatively and quantitatively.
MATERIALS AND METHODSA total of 86 mice of strain dd, of both sexes, ranging in age from 40 to 65 days, were used. The mice were deeply anesthesized with chloroform, and 3-5 ml of one of the following fixing fluids was injected into the peritoneal cavity: 5% formalin in 0.1 M phosphate buffer (pH 7.5) or 2% glutaraldehyde in 0.1 M cacodylate buffer (pH 7.5). After the peritoneal cavity was gently shaken or prodded, the total volume of the injected fluid containing peritoneal free cells was aspirated and examined in the following ways.Total number and size-distribution of peritoneal free cells were obtained with a Coulter counter (Model ZB...
