Strain 2, strain 13, or (2 × 13)F1 guinea pigs were immunized with human fibrinopeptide B, a 14 amino acid thrombin-derived fragment of the Bβ chain of fibrinogen (Bβ1-14), or the Bβ1-13 homologue, and in vitro T lymphocyte responsiveness was determined by the incorporation of 3H-thymidine. T cells from strain 2 or (2 × 13)F1 animals immunized with Bβ1-14 showed proliferative responses with Bβ1-14 but were unresponsive with Bβ1-13. Bβ1-13, Strain 13 Bβ1-14 immune T cells were unresponsive with both Bβ1-14 and 1–13. By contrast, T cells from strain 13 or (2 × 13)F1 guinea pigs immunized with Bβ1-13 produced proliferative responses with Bβ1-13 but not with Bβ1-14. Strain 2 Bβ1-13 immune T cells showed minimal or no responsiveness with Bβ1-13 or 1–14. Thus, responsiveness to Bβ1-14 is associated with strain 2 animals, and responsiveness to Bβ1-13 is associated with strain 13 guinea pigs. To determine the role of macrophages in presentation of Bβ1-14 or 1–13, T cells from (2 × 13)F1 guinea pigs immunized with Bβ1-14 or 1–13 were stimulated by antigen in association with macrophages derived from either parent. F1 T cells immunized with Bβ1-14 responded to Bβ1-14 in association with only strain 2 but not strain 13 macrophages. By contrast, Bβ1-13 immune F1 T cells responded with Bβ1-13 in association with only strain 13 but not strain 2 macrophages. These results are discussed with respect to the role of macrophages in selecting immunogenic determinants of peptide antigens for presentation to T cells.
The immune response of strain 2, strain 13, and (2 × 13)F1 guinea pigs was studied after immunization with human fibrinopeptide Bβ(hFPB), a 14 amino acid (Bβ1-14) thrombin-derived fragment of fibrinogen. Several weeks after immunization, strain 2 and (2 × 13)F1 antimals showed a positive anti-hFPB delayed-type hypersensitivity skin test and produced a dramatic hFPB-specific T lymphocyte proliferative response in vitro, as assessed by the incorporation of 3H-thymidine. Strain 13 animals immunized with hFPB did not produce an anti-hFPB skin test and showed little or no in vitro T cell proliferation with hFPB. Neither guinea pig strain produced detectable anti-hFPB antibody as determined by radioimmunoassay. Immune T cells were also tested for their ability to respond to several sequential synthetic homologues of hFPB. Strain 2 and (2 × 13)F1 T cells immunized with hFPB (Bβ1-14) were stimulated by fragments Bβ3–14, 5–14 and 7–14, but not by fragments Bβ1–13 and 9–14. In addition, strain 2 and strain 13 guinea pigs were immunized with the various homologues themselves and the immune T cells tested for responsiveness in vitro with hFPB and a battery of the fragments. Strain 2 T cells immunized with Bβ1–13 showed no proliferative response with Bβ1–14, 3–14, 5–14 and 7–14, and neglible stimulation with the homologous antigen Bβ1–13. After immunization with Bβ5–14 and 7–14, strain 2 T cells showed a proliferative response with Bβ1–14, 3–14, 5–14, and 7–14, but not with Bβ1–13. T cells from strain 2 animals immunized with B 9–14 were unresponsive with all homologues tested. T cells from strain 13 guinea pigs immunized with Bβ1–13 produced a dramatic proliferative response with Bβ1–13, but were unresponsive with Bβ1–14, 3–14, 5–14, and 7–14. Strain 13 animals immunized with Bβ5–14 and 9–14 showed no T cell response with any of the homologues tested, whereas Bβ7–14 immune strain 13 T cells produced a small response with Bβ7–14. These results are discussed with respect to T cell recognition of specific amino acid sequences of the fibrinopeptide molecule.
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