We have shown previously that the reactive oxygen species generated by washed human ejaculates originate from cells which can be isolated in the low density region of discontinuous Percoll gradients. In this study we have used a simplified two‐step (40/80%) Percoll gradient to separate human ejaculates (n=109) into two populations of spermatozoa, exhibiting either a high or a low capacity for reactive oxygen species generation. We have then examined the relationships between this activity and other properties of the isolated fractions, with particular emphasis on the presence of leucocytes, which we have quantified using a monoclonal antibody directed against the common leucocyte antigen. The low‐density cells recovered from the 40%/80% interface of the Percoll gradients, differed from the high‐density fraction in exhibiting significantly reduced sperm motility, poorer sperm morphology, and a considerably enhanced capacity for reactive oxygen species production (P<0.001). In six cases the elevated levels of reactive oxygen species generation were associated with leucocyte concentrations in excess of 1 times 106 per 107 sperm, suggesting that leucocytes enter the seminal compartment in an activated, oxygen‐radical generating, state. However, in the majority of cases exhibiting high levels of reactive oxygen species production, leucocyte numbers were low or absent and the semen profiles were unremarkable, except that seminal sperm concentrations tended to be low. These results suggest that the oxidative stress responsible for defective sperm function involves reactive oxygen species originating from two sources; the sperm and infiltrating leucocytes. Copyright © 1990, Wiley Blackwell. All rights reserved
