Immune sperm agglutination: are only motile spermatozoa involved?

Human sperm-agglutinating sera was examined using the tray agglutination technique (TAT) with whole diluted semen, and also with a suspension of only progressively motile spermatozoa-obtained from the same semen sample by the penetration of motile spermatozoa in an overlying medium layer. The titres of tail-to-tail (T) agglutinating sera were considerably lower with the latter sperm suspension, but head-to-head (H) agglutinating sera gave similar titres with the two types of sperm suspensions. Attempts to increase titres of T-agglutinating sera with only progressively motile spermatozoa were made by reducing the progression rate of the spermatozoa, and by increasing the concentration of the sperm cells. However, significant titre differences remained. Moreover, the agglutinates obtained were very small, and difficult to observe with the routinely employed magnification of x40. The lower titres still remained where seminal plasma was used as the penetration medium, indicating that a loss of coating antigen(s) was not the cause of lower titres. It seems likely that spermatozoa are attached to each other only weakly in T agglutination, much more weakly than in H agglutination. It is considered that immotile sperm cells that are present in whole diluted semen reinforce the T agglutination process, producing the higher titres.