Microvascular permeability to the F(ab')2 fragment of IgG in the male rat reproductive tract at puberty.

Development of contraceptive vaccines has recently raised much interest following the cloning of the sperm and oocyte components involved in the sperm-oocyte interaction. The main difficulty of immunocontraception in the male is the poor access of antibodies to the luminal compartment. As recent literature suggests that many substances are transported to the testis by receptor-mediated or fluid-phase transcytosis, the dependence of the transport of IgG on the Fc receptor was studied in the present investigation by comparing the penetration of whole IgG and the F(ab')2 fragment of IgG to the testis and epididymis. The maximum volume of distribution (Veq) for the F(ab')2 fragment was significantly higher than that for whole IgG in the testis of 30-60-day old rats, in the caput and cauda of 30- and 45-day old rats and the corpus of 45-day old rats. The speeds at which equilibrium between tissue extracellular fluid and serum was reached (K) for the F(ab')2 fragment and whole IgG were significantly different in the testicular capsule of the 60-day old, in the caput and corpus of the 45- and 60-day old and in the cauda of the 45-day old rats. The microvascular permeabilities (PE) to the F(ab')2 fragment were more than 2-fold higher than those to whole IgG in the testis of the 20-, 45- and 60-day old, in the testicular capsule of the 20- and 45-day old, in the caput of 20-, 30- and 60-day old and in the corpus of 20-day old rats. The PE to whole IgG was more than 2-fold higher than that to the F(ab')2 fragment in the cauda of the 45-day-old rats. The PE to the F(ab')2 fragment increased steadily from 20 to 60 days of age in the testis and caput, but in the corpus there was a more abrupt increase between 30 and 45 days of age. In the cauda, PE remained in the same range of magnitude throughout pubertal development. These results suggest that the F(ab')2 fragment reaches the lumen of the reproductive tract more easily than whole IgG from 30 days of age onwards in the testis, whereas in the caput, corpus and cauda epididymidis the rate at which F(ab')2 fragment reaches the lumen increases only temporarily at the time of appearance of spermatozoa in the lumen. Transport of IgG to the male reproductive tract is thus unlikely to be mediated by Fc receptors.