Immunosuppression of cell- and serum- mediated tumour-associated immunity in prostatic cancer by human seminal plasma

The immunosuppressive properties of the hormonal and/or secretory milieu or tumour-elaborated factors (in the case of carcinoma) of the prostate have been hypothesized as contributory to the natural history of prostatic cancer. The effect of normal human seminal plasma (HuSPl) on immunity to tumour-associated antigens and the 'arming' of normal peripheral blood leukocytes (PBL) by cytophilic antibody in the sera of patients with prostatic cancer have been evaluated by leukocyte adherence inhibition, a suggested in vitro correlate of cellular immunity. Significant (P < 0.01) suppression of immunity to malignant prostate ranging from 16 to 80% of the level of reactivity obtained with unincubated patients' PBL was observed in 22 (88%) of 25 patients following pre-incubation of their PBL with HuSPl. Similarly, pre-incubation of PBL from eight normal adults with HuSPl prior to 'arming' with sera from patients with prostatic cancer resulted in significant suppression of 'arming' by cytophilic antibody ranging from 10 to 60% of their level reactivity obtained with unincubated and 'armed' PBL and malignant prostate. Suppression of tumour-associated immunity by HuSPl provides further evidence to studies by others demonstrating SPl suppression of a range of in vitro immune responses in normal bovine, murine and human hosts. In addition to the possible biological implications of the immunosuppressive properties of SPl, e.g., as directed toward preservation of the species, whereby under normal conditions tolerance to spermatozoa in the male tract and in the female tract, following coitus, is maintained, it is hypothesized on the basis of collation of studies demonstrating experimental prostatic cancer from sensitization by spermatozoa and the relationship of prostatic cancer to repression of sexual activity, that SPl may play a significant role in the natural history of prostatic cancer.