The Journal of Immunology, Vol 143, Issue 6 1943-1947, Copyright © 1989 by American Association of Immunologists

ARTICLES

Isolation of homologous restriction factor from human urine. Immunochemical properties and biologic activity

LS Zalman, MA Brothers and HJ Muller-Eberhard
Research Institute of Scripps Clinic, Department of Immunology, La Jolla, CA 92037.

A soluble form of homologous restriction factor (HRF-U) was isolated from normal human urine. With respect to m.w. (65,000) and immunoblotting characteristics, it resembled membrane HRF (HRF-M) that had been isolated from human E membranes. The protein exhibited limited cross-reactivity with the channel-forming proteins of C and cytotoxic lymphocytes. It inhibited reactive lysis of E by human C5b-9. Inhibition occurred at the attachment stage of C5b-7 to target cells, rather than at the C8 or C9 stage of membrane attack complex assembly which is inhibited by HRF-M. In this respect, HRF-U acts analogously to S protein of serum, but no immunochemical relationship between these two proteins was detected. HRF-U might be derived from the soluble HRF detected in cytoplasmic granules of killer lymphocytes.

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