Macrophage-lymphocyte cluster formation in the medullary sinus of lymph node after immunization with sheep red blood cells (SRBC)

Development of cytoplasmic digitations between Leydig cells and testicular macrophages of the rat

Testicular macrophages and Leydig cells from adult animals are known to be functionally coupled. For example, secreted products from macrophages stimulate testosterone secretion by Leydig cells. In adult rat testes, structural coupling also exists between these cells. This coupling consists of cytoplasmic projections from Leydig cells located within cytoplasmic invaginations of macrophages. Although macrophages are known to exist in the testis in immature animals, it is not known when these digitations develop. The purpose of the present study was to determine whether the time of their development coincides with known maturational events that occur in Leydig cells, particularly during the peripubertal period. Testes from rats at 20, 30 and 40-days-of-age as well as testes from mature rats weighing more than 500 gm were prepared for ultrastructural analysis. It was found that digitations form between 20 and 30-days-of-age. These structures varied from simple tubular projections to complicated branched structures, suggesting that digitations are more than simple invaginations of microvilli into coated vesicles as previously described. Subplasmalemmal linear densities were also observed within macrophages juxtaposed to Leydig cells. Collagen was commonly observed between macrophages and Leydig cells in animals 20 days old. These studies demonstrate that although macrophages are present in the testis in maximal numbers at 20 days-of-age, they do not form junctions with Leydig cells until day 30. This is just prior to the major increase in secretory activity of rat Leydig cells that occurs during puberty.

Interactions of leukocytes with vessel walls and with other blood cells, studied by high-resolution intravital videomicroscopy of spleen

Visualization of circulating leukocytes in vivo is difficult because their optical density differs so little from that of plasma. We have obtained intravital microscopic images of leukocytes at high resolution in spleens of rats and mice by means of an inverted microscope with a 100 x oil-immersion lens; oblique lighting gave improved contrast. Photographic evidence and quantitative data describing the behaviour of lymphocytes, polymorphonuclear leukocytes (PMNs), and macrophages within the microvasculature are presented. Mean numbers of marginated lymphocytes in venous vessels ranged from 0.1 to 4.5 per 1000 microns 2 of wall surface, and speeds of rolling from 11 to 20 microns/sec. Adherence times of leukocytes to vessel walls were log normally distributed, median values being 30, 130, and 560 sec, for lymphocytes, PMNs, and macrophages, respectively. Mean speeds of migration along luminal surfaces were similar (7-19 microns/min) for all three types of cells. Lymphocyte migration outward through the venular wall, observed on two occasions, took 1-2 min. Median values for duration of adherence of RBCs and lymphocytes to macrophages were 1 and 42 sec, respectively. Phagocytosis of a lymphocyte was observed and took 3 min. Macrophages often underwent dramatic changes in shape, including formation of a pseudopod up to 155 microns in length. High-resolution intravital videomicroscopy of spleen has great potential for studying leukocyte behaviour, e.g., homing and migration of lymphocytes, and immunologically related macrophage-lymphocyte interactions in vivo.

Ultrastructural characteristics of the contact zones between Langerhans cells and lymphocytes

The present work was carried out to look for the ultrastructural substrate of the contact zones between Langerhans cells and lymphocytes. A high resolution electron microscopic analysis of the contact zones between Langerhans cells and lymphocytes was performed. The material used for this study was obtained from experimental contact dermatitis in mice, and human cervical squamous carcinoma and mycosis fungoides. Three types of cell-cell binding were found. Type I is a junction-like structure characterized by the presence of intercellular bridges. It is suggested that this contact might represent a fixation mechanism between the two cells. Type II is characterized by a glycocalyx-glycocalyx continuity. An immunological function--recognition and antigen presentation--is proposed for this type of contact. Type III is a septilaminar tight contact area which seems to be a gap junction. It is suggested that all these types of physical contact might be the morphological expression of interaction between antigen presenting cells and lymphocytes.

The structure of the sinus wall of the lymph node relative to its endocytic properties and transmural cell passage

The internal structure of cells lining the lymphatic sinus of the lymph node includes the presence of large bristle-coated vesicles, transfer tubules, and vesicular organelles for the uptake and intracellular disposition of endocytosed material. The lining cells of the sinuses phagocytose particulate material from the lymph in the same manner as the sinusoidal endothelium of the bone marrow takes up particulates from the blood and, thus, are similar in this respect to the endothelial lining of the bone marrow sinusoids. Transmission and scanning electron microscopic examination of the lymphatic sinus wall in rat lymph nodes show that the walls of the lymphatic sinuses are continuous and do not have permanent apertures allowing free communication between the extrasinusoidal and intrasinusoidal compartments in the lymph node. Migrating lymphocytes cross the lymphatic sinus wall intracellularly, i.e., through the body of the lining cell, by making a temporary migration pore, which closes after the cell has reached the lumen of the sinus. In addition there are sporadic aggregations of macrophages in transmural positions. The direction of their movement is unknown.