BINDING OF THE ANTI-HUMAN SPERM MONOCLONAL-ANTIBODY HS-11 TO BULL SPERMATOZOA IS CORRELATED WITH FERTILITY IN-VITRO

The present study aimed to determine if there is bull to bull variatio n in the binding of the anti-human sperm monoclonal antibody (MAb) HS- 11 to bull spermatozoa, and to investigate if there is any correlation between HS-11 binding to spermatozoa and in vitro fertility of the bu lls tested. Semen samples of a single collection (split frozen in 0.5- ml straws) from 8 dairy bulls were used. Swim-up separated motile sper matozoa were incubated in 90-mu l drops of capacitation medium (TALP+1 0 mu g/ml heparin) at 39 degrees C, 5% CO2, 95% air. At 0, 2, 4 and 6 h of incubation HS-11 was added (1:1000 final concentration), and the MAb binding was assessed by indirect immunofluorescence assay (IIFA). The HS-11 binding was indicated by a bright green fluorescence of the sperm acrosome region. In vitro-matured, good quality bovine oocytes w ere randomly allocated to spermatozoa of each bull for in vitro fertil ization. Sperm samples of 2 to 3 bulls were used in each trial until 4 replicates per bull were attained for IVF (n alpha 100 oocytes/bull) and IIFA experiments. Sperm capacitation status was assessed simultane ously using an egg yolk lysophosphatidylcholine- (LC) induced acrosome reaction assay. The binding of HS-11 to spermatozoa was maximum at 4 h of incubation in most (6/8) of the bull semen samples. Significant ( P<0.01) differences were observed between bulls in the binding of HS-1 1 to their spermatozoa (range 22+/-8 to 52+/-5%) at 4 h, but not withi n replicates. Similarly, variations (P<0.05) in the cleavage rate were also seen (range 22+/-9 to 58+/-7%) between bulls. The HS-11 binding and cleavage were significantly correlated (r=0.43; n=32; P<0.05). The highest percentage of spermatozoa underwent acrosome reaction in resp onse to LC treatment at the 4-h incubation period. This and the linear relationship between HS-11 binding and the cleavage rate observed in the present study together strengthen our earlier suggestion that the binding of the monoclonal antibody HS-11 to bull spermatozoa on a time -dependent manner, may indicate capacitation changes. We conclude that 1) between-bull differences exist in HS-11 binding to spermatozoa, an d in the cleavage rate, and 2) HS-11 binding to spermatozoa is correla ted with fertility, as determined by the cleavage of bovine oocytes ma tured and fertilized in vitro.