Effects of refeeding subsequent to starvation on the plasma cell population in the villous lamina propria of the rat small intestine.

The effects of refeeding subsequent to starvation on the plasma cell population in the lamina propria of the small intestinal villi were studied in adult rats utilizing the immunohistochemical method to detect IgA, IgM and IgG. Under normal conditions of stimulation, intestinal plasma cells (IPC) occur only as a sparse population. However, the present study demonstrated that extensive hyperplasia of IPC could be induced by refeeding after starvation. Starvation for a period of 4 to 6 days alone produced only a small change in the IPC population. In contrast, refeeding subsequent to starvation (for 4 to 6 days) was accompanied by a large increase in the population of IPC: the proportions of these cells among the lamina propria cells often rose to more than 50% within 3 or 6 days. The large majority of the proliferating IPC were found to express IgA, whereas cells bearing IgM or IgG occurred in extremely small numbers in the lamina propria. The mechanism whereby extensive IPC hyperplasia can occur in response to refeeding after starvation is discussed in relation to the possible promotion of transmission of antigenic macromolecules across the mucosal barrier induced by this procedure. It is also suggested that the origin of the proliferating IPC may be correlated with the B cell precursors in the germinal centers of the Peyer's, patches, which are more resistant to starvation than other lymphoid cells.

Intestinal mucosa and intra-abdominal lymphoid tissues of the platypus, Ornithorhynchus anatinus.

The morphological features of the intestinal mucosa and intra-abdominal lymphoid tissues of the platypus were examined. The mucosal surface of the intestine was characterized by the formation of large folds instead of the finger-like villi found in placental mammals. The lamina propria of the mucosal fold was well developed and contained numerous lymphocytes, expressing the lymphoid nature which is characteristic of the lamina propria of mammalian intestines. Although numerous well-developed Peyer's patches were observed in the ileum, solitary lymphoid nodules could not be found anywhere in the small intestine. Other intra-abdominal lymphoid tissues, particularly mesenteric lymphoid nodules, were well developed. However, each nodule represented a single follicle in contrast to the mammalian mesenteric lymph node which is composed of numerous follicles fused together. On the basis of the above findings, the tissues in question are considered to be at an evolutionary level preceding that of placental mammals.

Ia antigen expression by reticulum cells in lymphoid tissues and mesenchymal cells in the interstitium of the heart and liver of adult rats.

In an earlier series of studies on cellular labeling with [14C]adenine ([14C]A) in adult rats. Osogoe and his colleagues demonstrated the occurrence of certain cell types which are capable of incorporating [14C]A to a particularly great extent, such as the immature forms of either macrophage or fibroblast or reticulum cell lines. Further investigations have revealed that, among such cell types, a few fibroblastoid cells in the interstitium of the kidney and lung, as well as the proliferative reticulum cells in the intestinal lamina propria, express Ia antigen. In the present study, the reticulum cells in the lymphoid tissues and an appreciable number of mesenchymal cells in the interstitium of the heart and liver were also found to express Ia antigen. These two types of Ia-positive cells were characterized by a large cell body having a large euchromatic nucleus and abundant cytoplasm with dendritic processes. However, the mesenchymal cells were found in the interstitial tissue space of the organs, mostly scattered singly or occasionally grouped in small cell aggregations, without coexisting lymphoid cells. The biological significance of the Ia antigen expression by the two cell types, in particular the mesenchymal cells, is discussed in relation to their capacity for uptake of [14C]A.

Immunohistochemical study of intestinal lamina propria cells in the rat, with special reference to Ia antigen expression.

A previous study by Osogoe and Yanagi (1987a) has demonstrated that a large proportion of the lamina propria cells (LPC), mostly reticulum cells, in the core of the rat jejunal villi exhibit a strong labeling with [14C]adenine [( 14C]A). To obtain further information on such LPC, immunohistochemical detection of either Ia antigen or IgA on intestinal LPC was carried out in adult rats. It was found that almost all the LPC in the villous core of the small intestine express Ia antigen, and that in this area IgA-containing B cells also occur in unexpectedly large numbers. However, the number of Ia-positive non-B cells was greater than that of IgA-containing B cells which are also Ia-positive. Since the Ia-positive non-B cell population is composed mostly of reticulum cells, the above findings indicate that a large number of LPC, mostly reticulum cells, not only exhibit a strong labeling with [14C]A but also express Ia antigen. The biological significance of Ia antigen expression is discussed in relation to the proliferative activity of the cells.

Adenine uptake cells in the rat kidney with remarks on the expression of Ia antigen.

The patterns of [14C] adenine ([14C]A) incorporation into DNA by proliferative cells in the kidney were studied by the autoradiographic technique. It was revealed that, after 3 daily injections of [14C]A (1 microCi/g body weight each), a portion of the glomerular cells and a few fibroblastoid cells in the cortical intexstitium incorporated [14C]A into DNA to a remarkable extent. Such cells also incorporated [3H]thymidine, but to a lesser extent. The cells which incorporate [14C]A to a particularly great extent (adenine uptake cells) also occur in other tissues. Such cells are confined to a few cell types of either the macrophage or fibroblast or reticulum cell lines. This fact suggests that the adenine uptake cells observed in the glomerulus are also of a similar cell line and most likely mesangial cells. By immunohistochemical examination for Ia antigen, adenine uptake cells are divided into Ia-positive and Ia-negative types. The present examination showed that the major portion of adenine uptake cells in the glomerulus are Ia-negative, and it is suggested that these cells are analogous to the Ia-negative macrophages in the lung. This suggestion is supported by the fact that, in the glomerulus, colloidal carbon uptake cells (macrophage-like cells) are present in fairly large numbers. The Ia-positive cells seem to be of the same cell line as the adenine uptake cells that express Ia antigen in other tissues, such as septal fibroblasts in the lung.

Adenine uptake by rat connective tissue cells with special reference to macrophage precursors.

After 3 daily injections of [14C]adenine ([14C]A) (1 microCi/g body weight each) into young adult rats, the large majority of typical, spindle-shaped fibroblasts in the connective tissues of most organs showed almost no labeling, with the exception of a few weakly labeled ones. In contrast, in the interstitial connective tissues of pancreas and heart, unexpectedly numerous mesenchymal cells were found to exhibit especially strong labeling with [14C]A even after RNase treatment. Such cells had a large, round or ovoid, euchromatic nucleus and showed the blast-like appearance. The term mesenchymal cells was used to denote a special type of connective tissue cells that retain the potentiality of embryonic mesenchymal cells. Double labeling experiments using [14C]A and trypan blue by 7 daily injections (1 microCi/g body weight of [14C]A and 3 ml/rat of 0.5% aqueous solution of trypan blue each) disclosed that the mesenchymal cells exhibiting heavy [14C]A labeling did not ingest trypan blue at all. It was further revealed that, in addition to the mesenchymal cells, macrophages showing a remarkable trypan blue uptake were also labeled with [14C]A, though to a lesser extent than were the former cells. Moreover, transitional forms between the mesenchymal cells and macrophages were occasionally observed. The transitional forms were characterized by having the capacities not only for a fairly high rate of DNA synthesis but also of ingesting trypan blue, though to a slight extent. On the basis of the above findings, it can be stated that the mesenchymal cells showing heavy labeling with [14C]A are most likely the precursor cells of macrophages.