Search

CD8+ T cells can perform both Th 1 - and Th2-like functions by producing cytokines such as interferon- γ (IFN-γ) and interleukin-4 (IL-4), as well as the immune response down-regulating transforming growth factor-β (TGF-β), which are all involved in the development of experimental autoimmune myasthenia gravis (EAMG), a model for human MG. We have reported that depletion of CD8+ T cells results in the suppression of EAMG accompanied by the down-regulation of AChR-specific B cell responses and AChR-reactive IFN-γ secreting Th1-like cells. To identify the involvement of IFN-7, IL-4 and TGF-β in the development of EAMG after CD8+ T cell depletion, the expression of mRNA for these cytokines was studied in mononuclear cells from popliteal, inguinal and mesenteric lymph nodes, spleen and thymus by adopting in situ hybridization with complementary DNA oligonucleotide probes. Depletion of CD8+ T cells resulted in decreased levels of IFN-γ and IL-4 mRNA expressing cells in different lymphoid organs except thymus, but no change in the numbers of TGF-γ mRNA expressing cells. The results imply that the suppression of EAMG after depletion of CD8γ T cells is caused by decreasing the effector factors but not by increasing the suppressor factor(s). [ABSTRACT FROM AUTHOR]

In African trypanosomiasis the occurrence of antibodies to interferon-γ (IFN-γ) was studied in both humans and experimental rats. Sera from patients infected with Trypanosoma brucei gambiense showed increased levels of antibodies to IFN-γ as compared with controls from the same regions in Africa. In Sprague-Dawley rats infected with Trypanosoma brucei brucei an early appearance of IFN-γ-producing spleen cells was observed, followed by an increase in levels of antibodies against IFN-γ in the sera. Previously, IFN-γ has been found to play a crucial role in trypanosome infections in rats by promoting proliferation of Trypanosoma brucei brucei. The appearance of antibodies to IFN-γ in humans, as in rats, indicates that this cytokine is produced also in the human infection. Its parasitic growth-stimulating and pathophysiological effects on the organism may be reduced by the antibodies. [ABSTRACT FROM AUTHOR]

A protein factor that stimulates CD8+ lymphocytes to produce and secrete IFN-γ has been purified from Trypanosoma brucei brucei (T.b. brucei). This was accomplished by raising monoclonal antibodies (MoAbs) against a fraction of T.b. brucei obtained by gel filtration, which contained high levels of material inducing rat mononuclear cells (MNC) to IEN-γ production. MoAbs from four hybridomas strongly inhibited trypanosome-induced IFN-γ production. One of them (MO1) was used for purification of the trypanosome-derived lymphocyte triggering factor (TLTF) by affinity chromatography. SDS electrophoresis of the purified TLTF displayed a band of 42-45 kDa MW. Gel filtration of homogenates of whole parasites yielded several peaks of IFN-γ-inducing activity with a lowest MW of 41 -46 kDa. Bioactivity of all peaks was blocked by MO1, suggesting that a single molecule, or a single epitope of additional molecules, is responsible for the different peaks with IFN-γ-inducing activity. IFN-γ released from MNC stimulates T.b. brucei growth. Blocking of TLTF in vitro with MOI inhibited MNC supported growth of the parasites. To study the in vivo relevance of TLTF in the course of experimental African trypanosomiasis, MOI was used to treat rats and mice at different times after infection. Treatments instituted at different time-points after infection suppressed parasite growth, abrogated the IFN-γ production by splenocytes induced by the infection and prolonged survival of the animals. The data support the hypothesis that TLTF and IFN-y have a crucial regulatory function in the parasite host interactions and that these molecules influence the disease course during experimental African trypanosomiasis. [ABSTRACT FROM AUTHOR]

The cross talk between the central nervous system (CNS) and the immune system includes among others, the modulation of immune responses by the autonomic nervous system. Here, we investigated the effects of a splenic denervation on cytokine induction in early experimental African trypanosomiasis. Profiles of the cytokine mRNA expression for interleukin (IL)-4, interleukin (IL)-6, interleukin (IL)-10, interleukin (IL)-12, tumour necrosis factor (TNF)-alpha, tumour necrosis factor (TNF)-beta, transforming growth factor (TGF)-beta and interferon (IFN)-gamma were examined at 4 h, 8 h and 12 h postinfection (p.i.), and in noninfected controls. Only IFN-gamma and IL-12 were significantly expressed over noninfected controls. Already at 4 h p.i. both cytokines were expressed and showed more increased levels at 12 h. Sympathetic denervation of the spleen markedly reduced the mRNA expression for both IFN-gamma and IL-12. Con A was used as a positive control and showed an enhanced mRNA expression, which was also suppressed by a splenic denervation. To demonstrate that the mRNA expression had resulted in a cytokine production, we looked for the protein level of IFN-gamma at 4 h p.i. by immunohistochemistry and found increased levels of IFN-gamma, which was also inhibited by the denervation. Sham-operated animals exhibited similar responses as the nondenervated controls. Our data present for the first time very early kinetics for a cytokine gene expression during an experimental African trypanosomiasis. Furthermore, the data suggest a regulatory role for the autonomic nervous system on cytokine responses at both the mRNA and the protein levels.

A protein factor that stimulates CD8+ lymphocytes to produce and secrete IFN-gamma has been purified from Trypanosoma brucei brucei (T.b. brucei). This was accomplished by raising monoclonal antibodies (MoAbs) against a fraction of T.b. brucei obtained by gel filtration, which contained high levels of material inducing rat mononuclear cells (MNC) to IFN-gamma production. MoAbs from four hybridomas strongly inhibited trypanosome-induced IFN-gamma production. One of them (MO1) was used for purification of the trypanosome-derived lymphocyte triggering factor (TLTF) by affinity chromatography. SDS electrophoresis of the purified TLTF displayed a band of 42-45 kDa MW. Gel filtration of homogenates of whole parasites yielded several peaks of IFN-gamma-inducing activity with a lowest MW of 41-46 kDa. Bioactivity of all peaks was blocked by MO1, suggesting that a single molecule, or a single epitope of additional molecules, is responsible for the different peaks with IFN-gamma-inducing activity. IFN-gamma released from MNC stimulates T.b. brucei growth. Blocking of TLTF in vitro with MO1 inhibited MNC-supported growth of the parasites. To study the in vivo relevance of TLTF in the course of experimental African trypanosomiasis, MO1 was used to treat rats and mice at different times after infection. Treatments instituted at different time-points after infection suppressed parasite growth, abrogated the IFN-gamma production by splenocytes induced by the infection and prolonged survival of the animals. The data support the hypothesis that TLTF and IFN-gamma have a crucial regulatory function in the parasite-host interactions and that these molecules influence the disease course during experimental African trypanosomiasis.