Stimulation of activated rat T cells in vitro by Listeria monocytogenes antigens

Trichinella spiralis: selective intestinal immune deviation in the rat

In rats, infections with 100-2000 Trichinella spiralis muscle larvae lead to a prompt immunity that is expressed in parasite expulsion within 14 days. Rats infected with more than 2000 larvae display impaired immunity with rejection delayed by 50% (7 days) or more. Suppression is selective for expulsive immunity as the antifecundity response of rats is directly proportional to dose and is expressed sooner in heavily infected subjects. Suppression of intestinal expulsive immunity was suggested by the fact that, with low doses (2000 larvae or less), worm rejection was inhibited by cortisone, whereas cortisone inhibited antifecundity but had no discernable effect on worm rejection in high-dose infections. Evidence for local immune deviation as opposed to systemic immunosuppression was obtained in experiments using parabiotic rats. When one partner was infected with 6000 worms and the other with 200, the rat infected with 200 parasites showed earlier rejection than was seen in single controls infected with 200 worms. The prolonged survival of high-dose adults was not accompanied by a change in the site of worm residence in the gut. Immunological parameters such as serum antibody levels, the number of activated cells or specific anti-T. spiralis lymphocytes in thoracic duct lymph were all increased in a dose-dependent manner. These experiments therefore demonstrate a novel autoprotective mechanism by which adult T. spiralis selectively reduce the expression of expulsive immunity in the gut.

Genetic control of cell-mediated immunity in rats: involvement of RT1.B locus determinants in the proliferative response of T lymphocytes to Listeria antigens

The cellular requirements for Listeria monocytogenes antigen-induced, specific [3H]thymidine incorporation into lymphoid cells were analysed. Nylon-nonadherent lymph node and peritoneal exudate cells from infected athymic rats and mice failed to respond by proliferation, whereas control cells of thymus-bearing animals gave significant responses. In mice, cells expressing Thy-1 at a high density were required for the initiation of the proliferative response, but cells with lower density also participated in proliferation. Immune T cells alone failed to respond to L. monocytogenes antigen, but the addition of accessory cells provided optimal responses. These were nylon wool adherent, absent from thoracic duct lymph, but present in thymus and lymph nodes and particularly abundant in spleens of nonimmune rats. Accessory cells had to be matched at the B region of RT1, the major histocompatibility complex, to provide a stimulatory signal for L. monocytogenes antigen-specific T cells. Thus, the genetic restriction criteria were the same as for the transfer of delayed-type hypersensitivity to L. monocytogenes antigen, but differed from those controlling the transfer of acquired cellular resistance. The interaction between T cells and accessory cells could be blocked by alloantisera directed against Ia-antigens expressed on the accessory cell population. The study suggests that killed L. monocytogenes bacteria are presented by Ia-positive adherent cells in a RT1.B-restricted fashion to provide a proliferative signal for sensitized T cells.

In vitro proliferation of T lymphocytes from Listeria-infected rodents: assay conditions for rat peritoneal exudate cells and characterization of an inhibitor

Conditions favorable to [(3)H]thymidine incorporation into antigen-stimulated T lymphocytes from Listeria-infected rats have been established. In cultures of peritoneal exudate (T) lymphocytes purified twice with nylon-wool vigorous antigen-specific proliferation was observed within 2 days. Cultures of lymphocytes from nodes draining a subcutaneous Listeria-infection site differed in that back-ground proliferation was higher than for peritoneal exudate lymphocytes, and [(3)H]thymidine incorporation was maximal at day 3. A critical factor for the rate of proliferation was the lymphocyte-to-macrophage ratio; optimal cultures of peritoneal exudate lymphocytes contained 2 to 5% macrophages. Macrophages exceeding a proportion of 10% strongly, if not completely, inhibited [(3)H]thymidine incorporation into antigen-stimulated lymphocytes. Inhibition was associated with mononuclear cells, adherent to plastic or nylon-wool, of the stimulated or unstimulated peritoneal cavity. It was neither attributable to release of cold thymidine from macrophages nor to rapid degradation of particulate antigen by macrophages. The degree of inhibition reflected the metabolic activity of macrophages; on a cell-for-cell basis, heat-killed and glutaraldehyde-fixed macrophages were less inhibitory, and stimulated macrophages were more inhibitory than macrophages from the unstimulated peritoneal cavity.