Minor H Antigens Introduced on H-2 Different Stimulating Cells Cross-React at the Cytotoxic T Cell Level during in Vivo Priming

Abstract

The cellular basis of the cross-priming observed with minor histocompatibility antigens on H-2 different cells was investigated. Cytotoxic T cells induced against minor alloantigens show absolute H-2 restriction at the effector level ([⁵¹Cr]-release). That is, F₁(BALB/c × BALB.B) (H-2^d/b) cytotoxic cells induced by immunization with B10(H-2^b) cells are not able to lyse B10.D2(H-2^d) targets. But an injection of B10 cells does prime F₁ mice for a secondary cytotoxic response to B10.D2. The technique of inducing cytotoxic effector function polyclonally with Con A in the absence of alloantigen was used here to establish that such cross-priming reflects what happens at the cytotoxic cell level. It is shown that an F₁ animal previously injected with B10 cells has expanded pools of memory cytotoxic cells reactive with B10 and B10.D2. From this it is concluded that: a) minor H structures on B10.D2 and B10 do cross-react at the cytotoxic T cell level during in vivo priming, and b) because normal cells cross-prime whereas tumor cells do not, then the F₁ cytotoxic precursors are probably committed to respond to antigen on cells bearing either the maternal or paternal H-2 haplotype before they encounter antigen.

Cross-priming may be explained by foreign minor H antigens being presented to F₁ host T cells on the surface of host macrophages. Therefore priming is not restricted to the H-2 type of the injected cells but to both H-2 types of the F₁ host.