T-HELPER-1 (TH1) AND TH2 CHARACTERISTICS START TO DEVELOP DURING T-CELL PRIMING AND ARE ASSOCIATED WITH AN IMMEDIATE ABILITY TO INDUCE IMMUNOGLOBULIN CLASS SWITCHING

The respective production of specific immunoglobulin (Ig)G2a or IgG1 w ithin 5 d of primary immunization with Swiss type mouse mammary tumor virus [MMTV(SW)I or haptenated protein provides a model for the develo pment of T helper 1 (Th1) and Th2 responses. The antibody-producing ce lls arise from cognate T cell B cell interaction, revealed by the resp ective induction of C gamma 2a and C gamma 1 switch transcript: produc tion, on the third day after immunization. T cell proliferation and up regulation of mRNA for interferon gamma in response to MMTV(SW) and in terleukin 4 in response to haptenated protein also stares during this day. It follows that there is minimal delay in these responses between T cell priming and the onset of cognate interaction between T and B c ells leading to class switching and exponential growth. The Th1 or Th2 profile is at least partially established at the time of the first co gnate T cell interaction with B cells in the T zone. The addition of k illed Bordetella pertussis to the hapten-protein induces nonhapten-spe cific IgG2a and IgG1 plasma cells, whereas the anti-hapten response co ntinues to be IgG1 dominated. This indicates that a Th2. response to h apten-protein can proceed in a node where there is substantial Th1 act ivity.