A.I. Assis-Pandochi

Effect of Tityus serrulatus scorpion venom and its major toxin, TsTX-I, on the complement system in vivo

The effects of Tityus serrulatus venom and TsTX-I (Ts1 or gamma-toxin) on the lytic activity of the complement system (CS) were investigated in vivo. Serum classical pathway (CP) and alternative pathway (AP) activities were determined in sera of rats (200+/-10 g) injected i.p. with soluble venom (150 microg/kg), TsTX-I (150 microg/kg) or saline (control). The animals were sacrificed 0.5, 1, 2, 4, 24 and 48 h after injection. The results showed an increase in serum lytic activity of animals injected with venom, reaching values up to 70% above controls in CP activity and 120% in AP activity. These effects were biphasic with maximum values 1 and 24 h after venom injection. Similar effects were obtained for TsTX-I, but with lower intensity. Hematocrit values of all tested animals were determined to evaluate the effect of hemoconcentration on the lytic activity of the CS. It was observed that the maximum hematocrit value was obtained 1 h after injection and returned to normal values within 24 h. These data indicate that hemoconcentration can play a relevant role in the first peak of complement activity, but we cannot discard a direct action of the venom on the system during this period, since the serum venom concentration is maximal 15-30 min after envenomation. The high lytic activity of the serum observed after 24 h, period in which the hematocrit values are normal and no venom can be detected, may be consequence of the inflammatory process induced by the venom or toxin. The lytic activity of the serum of rats injected with venom, TsTX-I or saline was abolished when the serum was previously adsorbed on zymosan. These data confirm that the increase of the lytic activity of the serum induced by the venom or toxin is dependent on CS. These results show that CS is involved in the inflammatory process induced by the venom or toxin and consequently in the lung edema, hemolysis, leukocytosis, among other clinical manifestations of severe envenomation.

Effect of the period of treatment with a single dose of propylthiouracil on the antibody response in rats

Propylthiouracil (PTU) was employed in a fixed quantity to evaluate the effect of the period of treatment with this drug on the antibody response to sheep red blood cells in Wistar rats. Animals were treated for 8, 16, 30 and 90 days by intragastric route with 5 mg/day, and immunized 24 h following the end of treatment; other groups were treated for 21 days, and immunized on the 17th day of treatment. Animals were sacrificed 5 or 6 days following immunization; the primary response was evaluated by the number of plaque-forming spleen cells and in some cases also by enzyme-linked immunosorbent assay (ELISA). Secondary response of PTU-treated rats, immunized and boostered after 15 days, was evaluated by ELISA 3 days following the booster. RIA performed the measurement of T3 in animals treated for 16 days, immunized, and sacrificed after 1, 2, 3, 4 and 5 days following immunization. Results showed that treatment for 8 and 16 days increased production of antibodies, and for 30 and 90 days decreased this response. Thus, according to the period of treatment, the same dose of PTU stimulates or suppresses the antibody response. This biphasic effect of a single dose of PTU was independent of alterations of serum levels of T3 during the buildup of the immune response. These results contributes towards the understanding of the literature controversy regarding the effects of this drug on the immune response, and could be of interest for studies involving autoimmune processes in thyroid.

Activation of Complement Alternative Pathway in Rheumatoid Arthritis: Implications in Peripheral Neutrophils Functions

Evaluation of the respiratory burst induced by receptors Fc R and CR was carried out in peripheral blood neu- trophils (PBN) in rheumatoid arthritis (RA) patients with active and inactive disease. Simultaneously, cooperation be- tween these receptors and their expression, PBN chemotaxis, and complement system systemic activity were also investi- gated. Neutrophils were stimulated with IC-IgG opsonized with normal human serum (NHS) or not, or with IC-IgG op- sonized with RA human serum (RAHS). ROS production was increased in neutrophils of patients with active or inactive RA stimulated of IC-IgG opsonized with NHS compared to the response of the cells mediated by ICIgG. However, there was poor Fc R/CR cooperation in these RA neutrophils, as indicated by decreased ROS production upon stimulation with IC-IgG opsonized with RAHS. In the case of active RA patients, neutrophils presented significantly higher CR1 and CR3 expression, as well as slight elevation in CD32 and CD16 expression. Positive correlations between Fc R and CR, com- plement alternative pathway activation, and increased RA serum chemotaxic activity were only detected in active RA pa- tients. Taken together, these results indicate that several abnormalities of the complement system exist at the systemic level, namely impaired membrane receptor cooperation, alternative pathway activation, and presence of pre-existing chemoattractant factors in the serum, as reflected by the neutrophil function in the particular case of active RA patients. All, these abnormalities may synergistically contribute to RA pathogenesis.

Alternative complement pathway and factor B activities in rats with altered blood levels of thyroid hormone

Evaluating the activity of the complement system under conditions of altered thyroid hormone levels might help elucidate the role of complement in triggering autoimmune processes. Here, we investigated alternative pathway (AP) activity in male Wistar rats (180 ± 10 g) after altering their thyroid hormone levels by treatment with triiodothyronine (T3), propylthiouracil (PTU) or thyroidectomy. T3 and thyroxine (T4) levels were determined by chemiluminescence assays. Hemolytic assays were performed to evaluate the lytic activity of the AP. Factor B activity was evaluated using factor B-deficient serum. An anti-human factor B antibody was used to measure factor B levels in serum by radial immunodiffusion. T3 measurements in thyroidectomized animals or animals treated with PTU demonstrated a significant reduction in hormone levels compared to control. The results showed a reduction in AP lytic activity in rats treated with increasing amounts of T3 (1, 10, or 50 µg). Factor B activity was also decreased in the sera of hyperthyroid rats treated with 1 to 50 µg T3. Additionally, treating rats with 25 µg T3 significantly increased factor B levels in their sera (P < 0.01). In contrast, increased factor B concentration and activity (32%) were observed in hypothyroid rats. We conclude that alterations in thyroid hormone levels affect the activity of the AP and factor B, which may in turn affect the roles of AP and factor B in antibody production.