Specificity of the inhibitory effect of a grand-multipara serum on MLC reactions and on responses to PHA, PWM and PPD.

An MLC reaction inhibiting serum from a grand-multiparous woman (16 successful pregnancies) is described. The serum producer had the HLA antigen A3;Bw35/Aw19;B18;Dw2 and her husband the antigens A28;Bw35/Aw16;B18;Dw2, and they responded to each other in one-way MLC. The serum had the following characteristics: (1) it inhibited many but not all donors as stimulators in MLC; (2) it usually inhibited these same donors as responders in MLC, but clearly to a lesser degree and with a much lower titre; (3) the inhibition of the stimulating function followed HLA haplotypes in families, and seemed to have HLA-D associated specificity, inhibiting HLA-Dw3 and Dw6 homozygous but not HLA-Dw2 or Dw4 homozygous cells as stimulators; (4) it inhibited more strongly the PWM and PPD responses than the MLC responses of relevant cells; (5) the IgG fraction of the serum had characteristics similar to the non-fractionated serum; (6) the inhibitory effect on MLC reactions and PWM and PPD responses was not absorbable by specific red blood cells or platelets, but could be removed or diminished by specific lymphocytes; (7) the serum was not cytotoxic in the complement-dependent test against non-fractionated mononuclear cells or enriched B-lymphocytes. The findings and the possible biological and clinical significance of human Ia-like antibodies are discussed.