HIGH T3 LEVELS ALTERED THE ACTIVITY OF FACTOR B OF COMPLEMENT SYSTEM

BITENCOURT C. S.(1), AZZOLINI A. E. C. S.(1), PANDOCHI A. I. A.(1)

(1)Departamento de Física e Química, FCFRP-USP, Ribeirão Preto, SP, Brasil

Previous studies have shown that hypothyroidism affects the complement system (CS), increasing the lytic activity of the alternative pathway (AP). In accordance to this observation the aim of the present study was to investigate if the hyperthyroidism induced in rats by triiodotironine (T3) would also affect complement. Rats received 0.15 to 50mg of T3 by gavage during periods of 3-14 days. The lytic activity of CS was evaluated by hemolytic assay measuring time required for 50% of lysis to occur (t1/2). The activity of factor B was evaluated using serum depleted of B factor (RB) in a hemolytic assay. The lytic activities of classical/lectin pathways were not significantly altered at any time or T3 dose evaluated. The dose of 0.15mg reduced AP activity (increased t 1/2 values) after 7 and 14 days of treatment. These alterations showed statistical significance (Annova and Dunnet test). The effect on AP activity was dependent of the dose and the period of treatment. The factor B activity was altered in the conditions of reduced AP. Hyperthyroidism induced by T3 affects CS reducing AP lytic activity due to reduced activity of factor B; this effect is opposite to that observed in hypothyroidism. The effect of the T3 level on CS may be considered in certain conditions such as in autoimmune processes involving the thyroid gland.

KEY WORDS: Complement System, hyperthiroidism, factor B

FINANCIAL SUPPORT: CAPES

CORRESPONDENCE TO:

Claudia da Silva Bitencourt, FCFRP-USP, Avenida do Café s/n, Ribeirão Preto, (SP), CEP 14.040-930. Email: claubitencourt@yahoo.com