In vitro fertilization: increased VLA (very late antigen) integrins and fibronectin after acrosome reaction

The pattern of detectable adhesion molecules (AM) on human ejaculated spermatozoa used for in vitro fertilization (IVF) of human oocytes was evaluated. The percentage of spermatozoa with the alpha chains 3, 4, 5, and 6 of the integrins (also called very late antigens, VLA alpha 3, 4, 5, 6), the alpha V and the beta 3 chains, as well as the matrix proteins laminin and fibronectin, were determined by flow cytometry using monoclonal antibodies against integrins and matrix proteins before and after the acrosome reaction. This reaction was induced by the low-temperature method according to P. Sanchez, E. Töpfer-Petersen, R. J. Aitken, and W. B. Schill (1991, Andrologia 23:197-203) and monitored by the binding of FITC-conjugated Pisum sativum agglutinin. Twenty-three of 34 investigated semen samples fertilized at least one oocyte (fertile group) and 11 samples did not induce a pronucleus formation or cleavage of an oocyte (infertile group). Significant differences in the classical semen parameters between both semen sample groups could be shown only for the percentage of progressively motile spermatozoa (p = .046, U test). The spermatozoa of the fertile group showed a significantly higher expression of VLA alpha 3 (p = .045) and fibronectin (p = .048). Additionally, after the loss of the acrosome a significantly higher expression of alpha 4, alpha 5, and alpha 6 chains of integrins (p < .05) was detected in the fertile semen group. In contrast, the inducibility of the acrosome reaction differed only to a nonsignificant extent (p = .094). These data suggest that spermatozoa showing a higher expression of the alpha chains of the integrins after the acrosome reaction have a better fertilization rate in vitro.