ABSTRACT
TwodifferentstructuralpolymorphismsforCRlhavebeendescribed.Thefirstresultsfrom differentglycosylationoftheCR1ontheRBCsandothercellsofthesameindividual(25).A secondallotypicpolymorphismistheresultoffourautosomalcodominantallelesthatcodefor CR1receptorshavingdifferentnumbersofthelonghomologousrepeats(reviewedinref.26). Thisresultsinallotypesthatdifferbymolecularweightincrementsof30,000-50,000d (correspondingtothelonghomologousrepeats).Thecommonestallotype,F(alsoknownas A)(genefrequency0.81)hasfourlonghomologousrepeats,whereastheS(alsoknownasB) allotype(genefrequency0.2)hasfive.TworareallotypesF'(alsoknownasC)andDare known.BecauseeachofthelonghomologousrepeatsencodesaspecificbindingsiteforC3b andC4b,itislikelythatthedifferentallotypesmayhavedifferentaffinities/capacitiesforthe bindingofcomplementcontainingimmunecomplexes(26).
