Immune recognition of serum albumin-XIV. Cross-reactivity by T-lymphocyte proliferation of subdomains 3, 6 and 9 of bovine serum albumin

Recently, we have shown that, with rabbit antibodies against BSA, the BSA fragments 115-184, 307-385 and 505-582 (essentially corresponding to subdomains 3, 6 and 9 of BSA) exhibit a cross-reaction which increases remarkably with the time antisera are obtained after the initial immunization. In the present report, we have examined whether this cross-reaction at the B-cell level takes place also at the T-cell level. Optimum conditions for T-cell proliferation to BSA and the three fragments were determined in terms of priming dose, challenging dose, time lymph nodes are obtained after immunization and finally duration of culture. Several strains of mice representing independent haplotypes and recombinant strains were examined for their responsiveness to BSA by T-lymphocyte proliferation, performed in the respective preimmune sera of the same mice. This afforded the identification of high-and low-responder strains to BSA. It was determined that the immune response to BSA is controlled by genes in the I-A subregion of the H-2 gene complex with some slight non-H-2 influences. In order to avoid the possibility of a genetic exclusion of response to a given antigenic site and to improve the chance of total site recognition, two high-responder strains (B10.M and B10.G) were crossed. Antibodies raised in (B10.M × B10.G)F₁ mice recognized subdomains 3, 6 and 9 and these were found to be cross-reactive. Specific ¹²⁵I-labelled antibodies isolated on a given subdomain-adsorbent were bound very well by adsorbents of the other two subdomains. T-cells from the F₁ mice that had been primed with subdomain 3 responded to subdomain 3 and were also high responders to subdomain 6 and intermediate responders to subdomain 9. After priming with subdomain 6, the T-cells responded equally as well to subdomains 3 or 6 and slightly to subdomain 9. Finally, priming with subdomain 9, gave T-cells that responded to subdomain 9 and also gave high responses to subdomains 3 or 6. It was concluded that the cross-reactions originally observed at the B-cell level also take place at the T-cell level.