The role of thymic accessory cells in cytokine production and in the intra-thymic T cell differentiation pathway

Intrathymic T lymphocyte differentiation proceeds from complex interactions between prothymocytes of bone marrow origin and cells of the thymic stroma, epithelial cells and "acessory" cells (macrophages and/or interdigitating cells). The present paper describes the role of the accessoty cell compartment in this intrathymic process. Acessory cells produce factors which are involved in thymocyte proliferation (interleukin 1, prostaglandins, deoxynucleosides). Cell-cell interaction between "accessory" cells and thymocytes is required for the regulation of interleukin production. Prothymocytes, the precursors of all thymocyte subsets, need the accessory cell compartment for their IL2 dependent proliferation and their differentiation. Accessory cells of the thymic stroma may be involved in the intrathymic selection process at the prothymocyte level.

Differentation of the fat body cells in the precocius adults of Schistocerca gregaria: regulation of polyploidy by juvenile hormone

Precocious adults from 2nd and 3rd instar larvae of the desert locust Schistocerca gregaria were used to assess the competence of their fat body to synthesize DNA in response to a juvenile hormone analog (JHA), hydoprene. Autoradiographic studies show that JHA stimulates DNA synthesis since a significant proportion of the fat body nuclei are labelled after treatment with 100 or 200 µg of JHA. Maximum DNA synthesis occurs 24 h after treatment with 100 µg of JHA. The nuclear ploidy classes of the precocious adults from 3rd larvae are similar to those of 1-d-old normal adults, but treatemnt of these precociuos adults with µg of JHA doubles the DNA content resulting in enhanced ploidy classes which resemble those of 10-d-old normal females. In the precocious adults that emerged from 2nd instar larvae the ploidy classes are higher than those of 1-d-old normal adults, and treatment of these precocious adults with JHA results in a further increase in the DNA content of the fat body nuclei leading to the formation of high percentages of 16C and 32C nuclei. The results of these studies suggest that any model on the mode of action of JH should recognize this phenomenon of JH-induced polyploidization in the fat body nuclei.

In vivo kinetics of eosinophils and mast cells in experimental murine Schistosomiasis

During the schistosomiasis infection there is a [quot ]dance of the cells[quot ], varying from site to site and related to the time of infection. 1 - Eosinophil levels exhibit a bimodal pattern, with the first peak related to the egg deposition and maturation and increased Kupfferian hyperplasia; the second peak precedes the death of some adult worms; 2 - The peritoneal eosinophilic levels are inversely proportional to the blood eosinophilic levels; 3 - Eosinopoiesis in the bone marrow begins at day 40, reaching the highest levels at day 50 and coincides with hepatic eosinophilic and neutrophilic metaplasia; 4 - Peritoneal mast cell levels present a bimodal pattern similar to the blood eosinophils, and inverse to the peritoneal eosinophils. They also show a cyclic behaviour within the hepatic and intestinal granulomas. Integral analysis of the events related to the eosinophils in the blood, bone marrow, peritoneal cavity and hepatic and intestinal granulomas allows the detection of two important eosinophilic phases: the first is due to mobilization and redistribution of the marginal pool and the second originates from eosinophilic production in the bone marrow and liver. The productive phase is characterized by an increase in the number of eosinophils and monocyte/macrophages, and a decrease in neutrophils and stabilization of megakariocytes and erithroid lineages.

Reduced capacity of peritoneal exudate cells for oxidative killing of Schistosoma mansoni schistosomula

Peritoneal exudate cells from mice infected with Schistosoma mansoni (S-PEC) can kill schistosomula in vitro in the presence of immune serum. S-PEC produce a low level of respiratory burst, and schistosomula mortality in their presence is not reduced when exogenous antioxidants are added, suggesting that with S-PEC, oxidative killing is not important. Hydrogen peroxide (H2O2) and superoxide production by S-PEC, and cells from BCG and thioglycollate (THGL) injected non-infected mice, non-specifically stimulated with opsonized zymosan, were measured. Levels of H2O2 produced by S-PEC were significantly lower than BCG or THGL PEC, and were below the H2O2 threshold for schistosomula killing. This resulted in lower levels of cell-mediated killing of schistosomula in vitro by S-PEC than by BCG or THGL PEC. Superoxide levels, however, were similar between the three cell populations. The efficiency of PEC to kill schistosomules in vitro correlated with H2O2 rather than superoxide levels. The lower tolerance of schistosomula, compared to adult S. mansoni to GSH depleting agents increases their sensitivity to oxidative attack and resulted in higher levels of cell-mediated killing in vitro.

Cell mediated immunity in Chagas' disease: Trypanosoma cruzi antigens induce suppression of the in vitro proliferative response of mononuclear cells

The partial suppression of the cell-mediated immune response by Trypanosoma cruzi antigens in patients with Chagas' disease is demonstrated in a costimulation assay with T. cruzi antigens and Mycobacterium tuberculosis purified protein derivative (PPD) or Tetanus toxoid (TT). ononuclear cells from 13 patients with chagasic infection without evidence of heart disease, 10 patients with chagasic cardiomyopathy and 7 healthy blood donors were stimulated with antigen A (autoclaved epimastigotes), PPD, TT, PPD + A, PPD + TT and TT + A. The average percentage of suppression induced by costimulation of mononuclear cells with PPD and antigen A was 47.1% in patients with chagasic infection without heart disease (INF), 38.8% in patients with chagasic cardiomyopathy (CDM) and 23.3% in healthy controls. Similar values were observed when living trypomastigotes were used. A costimulatory study with PPD and TT, PPD and A and TT and A was carried out in 8 patients with chagasic infection, in order to evaluate the possibility that this difference could be due to a nonspecific inhibitory effect. The mean suppression induced by TT + PPD was -8.9, with TT + A was 52.7 and with PPD + A was 50.1. The data reported show that T. cruzi antigens induce a specific suppression of the proliferative responseof mononuclear cells, that might be relevant to the persistence of the parasite in the host.