In Vivo Administration of Antibodies Against Type I Collagen in Rat: The Specific Accumulation in Spleen

[¹²⁵1]-labelled rabbit antibodies against rat type I collagen and non-immune IgG were injected into rat circulation. The kinetics of their clearance and the biodistribution in different organs were studied. Both preparations showed very similar clearance rate, the kinetics fitting bi-exponential approximation with characteristic parameters t_1,1/2 = 201 ± 20 min before 320 min and t_1,1/2 = 1350 ± 450 min at times over 320 min for antibodies and 258 ± 45 min and 890 ± 140 min for IgG. The specific affinity of the circulating antibodies did not decrease within 24 hours. The antibodies were specifically accumulated in spleen, where their accumulation was 5-fold higher than that of nonimmune IgG. Accumulation of antibodies was maximal 3 hours after the injection. The localization ratio (i.e. the ratio of the amount of the antibodies per g of tissue to that per g of blood) reached a maximum 24 hours after the injection and remained stable for 120 hours. Immunofluorescent staining of spleen sections resulted in a bright fluorescence of dense collagenous structures in the trabeculae and in the wall of the central follicular arterium, bright spot fluorescence in the marginal zone of the follicle, and diffuse fluorescence in the red pulp. These findings suggest an unusually high accessibility of collagen type I in spleen to circulating blood plasma components.