Passive allograft enhancement by subclasses of polyclonal antibodies directed toward restricted regions of the major histocompatibility complex.

Two parameters of enhancing major histocompatibility complex (MHC) antibodies, previously separately studied, namely, Ig class and antigen specificity, have been treated simultaneously. In the experimental model used, Sa 1 tumor cells, indigenous of A/J (H-2a) were grafted on CBA (H-2k) or C57BL/Ks (H-2d) mice. Immune sera specific for the H-2 K/D- or H-2 I coded antigens of the A/J haplotype (anti-Kk, or IAk, IBk, IJk, IEk, or ICd, Sd, Gd, or Dd) and their immunoglobulin fractions (separated on protein A-Sepharose columns) were injected either i.v. or locally as mixture with the challenging Sa 1 cells. Within the limits of the studied system, the following results were obtained: (1) Sa 1 cells do possess Iak antigens at their surface detected by C-dependent cytotoxicity; no ICd, Sd, or Gd products were detected. (2) The bulk of enhancing activity is concentrated in IgG1 anti-K/D antibodies (anti-Dd when Sa 1 was grafted on CBA mice and anti-Kk, on C57BL/Ks). (3) Anti-Iak antibodies have some activity on Sa 1 cells grafted on C57BL/Ks mice. This activity is significant for IgG1 anti-Iak and suggestive for IgG2 of the same specificity. (4) No enhancing activity was detected in the other antibodies: IgG2 anti-Dd, IgG2 anti-Kk, IgG1, or IgG2 anti-ICd, Sd, Gd as well as in fractions containing IgM and IgA antibodies directed against any studied portion of the MHC products. This results are discussed in terms of the mechanisms involved in enhancement.