AN INNATE NATURAL ANTIBODY IS REACTIVE WITH A CRYPTIC SEQUENCE OF LACTOFERRIN EXPOSED ON SPERM HEAD SURFACE

Lactoferrin (LF), an 80-kDa glycoprotein of ubiquitous occurrence in b ody fluids, is multifunctional and capable of assuming different confi gurations to serve those functions, The capacity of LF to undergo endo cytosis and;he recent demonstration of LF binding to sequence specific DNA indicate that a function or capability of LF, in addition to iran chelations, bacteriostasis, and receptor-specific lymphocyte binding, may be that of gene activation or silencing. The data of this report present a human physiological system, that of sperm entry into the ooc yte in performance of fertilization in which, since LF is a component of the sperm protein coat, that capability could be expressed, However the configuration of LF in that locus is one in which a revealed cryp tic sequence provides the specific binding site for a natural antibody present: in the fertilization milieu. The presence of that antibody s uggests that a system of control of the potential interaction of LF wi th the intra-ooplasmic DMA, that of gametes or pronuclei, is operative . The configuration of LF on the sperm surface and designation of the reactive site for the natural antibody were enabled by a monoclonal an tibody secreted by a hybridoma derived from a human cord blood B cell, Thus, in addition to information concerning the molecular flexibility of LF, these observations support the proposition that the repertoire of natural antibodies provides an innate homeostatic system, with eac h antibody serving a specific role.