Stimulation of rat macrophage interleukin 1 secretion by plasma fibronectin

Purified plasma fibronectin (Fn) enhanced the secretory activity of rat peritoneal exudate macrophages as measured by 35S-methionine incorporation into protein released into culture supernatants. Enhancement of protein secretion was dose-dependent and increased with time in culture. Addition of various concentrations of supernatant from cultures of macrophages with Fn resulted in a significant increase in thymocyte proliferation elicited by phytohaemagglutinin. The stimulatory activity of the supernatant was Fn dose-dependent and increased with increasing concentrations of macrophages. This thymocyte stimulatory effect was not due to the presence of Fn in the culture supernatant or to the minimal contamination with endotoxin detected in the Fn preparations. These data suggest that the inflammatory macrophage interaction with Fn results in the release of interleukin-1. They also are consistent with the reported ability of Fn to stimulate lymphocyte transformation.

Induction of lymphocyte blast transformation by purified fibronectin in vitro

Purified rat plasma fibronectin (Fn) induces a dose-dependent, nonspecific proliferation of lymphoid cells isolated from spleen and lymph nodes, but has no effect on thymocytes. Proliferation of cells occurred after 4 to 5 days of incubation and was generally 5- to 10-fold greater than control cells cultured without Fn or in the presence of the same concentrations of rat serum albumin. The responding cell appears to be the T cell and requires the presence of adherent accessory cells (macrophages). Although purified T and B cells failed to demonstrate a significant increase in blastogenesis in the presence of Fn, reconstitution of T, but not B, cells with irradiated peritoneal exudate macrophages restored the stimulatory effect of Fn. Furthermore, comparison of the effect of various concentrations of macrophages on the restored T cell response shows that proliferative activity in the presence of Fn is dependent on a critical number of macrophages. Adding higher numbers of macrophages beyond the optimal concentration results in a sharp decline in lymphocyte responsiveness to Fn, although the proliferation of control cells continues to increase at these macrophage concentrations. Macrophages pulsed with Fn for 1 hr failed to evoke an increase in T cell responsiveness after 3 or 5 days of incubation. In addition, incubation of Fn-pulsed T cells with macrophages that had been precultured with or without Fn also failed to result in T cell activation. The effect of Fn on T lymphocyte transformation appears to be mediated indirectly through its interaction with the macrophage, because 125I-Fn, which shows significant binding to peritoneal exudate macrophages, fails to interact with purified T cells. Radiolabeled Fn also demonstrated little or no binding activity for unseparated lymph node cells.

Induction of lymphocyte blast transformation by purified fibronectin in vitro

Purified rat plasma fibronectin (Fn) induces a dose-dependent, nonspecific proliferation of lymphoid cells isolated from spleen and lymph nodes, but has no effect on thymocytes. Proliferation of cells occurred after 4 to 5 days of incubation and was generally 5- to 10-fold greater than control cells cultured without Fn or in the presence of the same concentrations of rat serum albumin. The responding cell appears to be the T cell and requires the presence of adherent accessory cells (macrophages). Although purified T and B cells failed to demonstrate a significant increase in blastogenesis in the presence of Fn, reconstitution of T, but not B, cells with irradiated peritoneal exudate macrophages restored the stimulatory effect of Fn. Furthermore, comparison of the effect of various concentrations of macrophages on the restored T cell response shows that proliferative activity in the presence of Fn is dependent on a critical number of macrophages. Adding higher numbers of macrophages beyond the optimal concentration results in a sharp decline in lymphocyte responsiveness to Fn, although the proliferation of control cells continues to increase at these macrophage concentrations. Macrophages pulsed with Fn for 1 hr failed to evoke an increase in T cell responsiveness after 3 or 5 days of incubation. In addition, incubation of Fn-pulsed T cells with macrophages that had been precultured with or without Fn also failed to result in T cell activation. The effect of Fn on T lymphocyte transformation appears to be mediated indirectly through its interaction with the macrophage, because 125I-Fn, which shows significant binding to peritoneal exudate macrophages, fails to interact with purified T cells. Radiolabeled Fn also demonstrated little or no binding activity for unseparated lymph node cells.

Modulation of rat lymphocyte transformation by plasma fibronectin

Purified rat plasma fibronectin (Fn) was studied for its ability to influence nonspecific lymphocyte transformation to various mitogens. Fn added to lymph node cells (LNC) stimulated with phytohemagglutinin (PHA), concanavalin A (Con A), or bacterial lipopolysaccharide (LPS) resulted in a noncytotoxic dose-dependent inhibition of the blastogenic response. Effective inhibition (greater than 50%) of LNC responses to PHA and LPS occurred with concentrations of Fn that ranged from 10-50 micrograms/culture. The proliferative response to Con A was less affected by the presence of Fn: 50% inhibition was observed only with the highest concentration of Fn studied. Fn at low concentrations was more effective than Fn-depleted plasma in inhibiting lymphocyte responses to PHA. Optimal expression of the regulatory activity of Fn occurs during and following the peak proliferative period for both PHA and LPS responses. In order to evoke maximum inhibition it is necessary for Fn to be present within 12 hours following stimulation of LNC with mitogen. Inhibition does not appear to be the result of Fn-mitogen complexes which reduce the amount of mitogen available for stimulation, since increasing concentrations of either PHA or LPS did not significantly reduce the inhibitory effect. Furthermore, inhibition was not influenced by the concentration of fetal calf serum present in the culture medium. Thus, Fn may function as an important nonspecific immunoregulatory factor at inflammatory sites and in areas of tissue repair.

The development of transport ability by embryonic follicle-associated epithelium

The development of transport ability by follicle-associated epithelium was studied in embryonic chick bursae. Developing lymphoid follicles were divided into three morphological types to determine the relationship of epithelial function to lymphoid development. Transport ability was first observed on day 13, two days earlier than obvious morphological evidence of follicle-associated epithelial development. Functional differentiation of the epithelium was, however, closely associated with lymphoid development rather than a day-specific developmental event. It is probable that the lymphoid cells have an inductive influence on the development of the overlying epithelium. Evidence of early embryonic transport by relatively undifferentiated epithelium also suggests that lymphoid development in the bursa may be influenced by epithelial transport.

The role of epithelial cells in gut-associated immune reactivity

Epithelial cells and their products are essential participants in both initial and final stages of reactivity to foreign materials in the gut lumen. Follicle-associated epithelial cells, called "M"-cells by others, more efficiently transport antigens from the lumen than do columnar absorptive cells. Epithelial cells degrade antigens intracellularly. The presence of Ia-like antigens on epithelial cells of the gastrointestinal tract and thymus suggests a role in antigen presentation. Actively phagocytic macrophages are present within the epithelium of Peyer's patches and appendix, providing antigen degradation and presentation. Follicle-associated epithelial cells transport materials from lamina propria into intestinal lumen. Therefore, FAE cells are capable of bidirectional transport. Plasma cells are located within and immediately beneath the epithelium of Peyer's patches and appendix, where defects in the basal lamina indicate diminished capability for molecular selection. Transmission of antibodies into the lumen would modulate further antigen uptake and provide for interaction with organisms.

The influence of embryonic testosterone treatment on bursal epithelial pinocytotic activity

Developing White Leghorn chicks were treated with testosterone propionate in ovo to effect a partial chemical bursectomy. After hatching, birds were administered carbon particles or horseradish peroxidase via the cloaca, and the transport of these tracers by the bursal epithelium was examined. Uptake of both tracers was inhibited in the treated when compared to untreated birds. The degree of development of interaction between bursal epithelium and underlying lymphoid tissue appeared to play a major role in determining ability of the epithelium to transport these tracers. Epithelium associated with follicles possessing medullary and cortical divisions was able to transport, while intraepithelial follicles or regions of the epithelium overlying diffuse lymphoid tissue did not transport either carbon or horseradish peroxidase. Bursal function in regional defense of the gut may depend on a local interaction of bursal epithelium with lymphoid, and perhaps other cell types.