Soluble FcγRIII (CD16) and Immunoglobulin G Levels in Seminal Plasma of Men with Immunological Infertility

Abstract

Receptors for the Fc region of the immunoglobulin G (IgG) (Fc gamma R) have been recognized as a link between humoral and cellular immune responses. A soluble form of FcγRIII (CD16) has been found in seminal plasma (SP), which may modulate immunosuppression of antisperm immune responses in the male and female reproductive tracts. SP from some individuals apparently have lower levels of FcγRIII, but it is not known whether the diminished activities are due to low receptor concentration or steric interference from IgG. To test the hypothesis that different levels are due to steric interference, relative levels of FcγRIII were measured in SP using monoclonal antibody 3G8 in an amplified enzyme‐linked immunosorbent assay (ELISA) system. Men who were positive for antisperm antibodies (ASA) by Sperm Mar and direct immunobead assay (N = 26) and negative for ASA (N = 26) were tested. Individuals who were ASA positive had lower detectable levels than those who were ASA negative (t = 1.99, P = 0.05). Therefore, variation in FcγRIII levels may be due to steric interference from IgG. IgG subclass concentrations in SP of both groups were determined using an ELISA method and compared to FcγRIII levels. Slight correlations were seen for lgG1 (r2 = 0.237, P < 0.001), IgG2 (r2 = 0.204, P < 0.001), and total IgG (r2 = 0.299, P < 0.001) in relation to FcγRIII levels in ASA‐negative SP specimens. We conclude that ASA‐positive SP has lower detectable levels of FcγRIII and that some variability in ASA‐negative SP can be attributed to variance in IgG subclass levels, especially IgG1 and IgG2. Therefore, we can conclude that lower levels of FcγRIII in some SP specimens are due to steric interference from IgG.