Peptide-induced T cell clones: specificity, MHC restriction, proliferation and cytokine pattern as a function of different stimulations.

CD4+ T cell clones were generated to tetanus toxin or to two tetanus toxin-derived peptides p2 (AA 830-834) and p30 (AA 947-976). 11 of the 24 p30-specific clones reacted to shorter p30 subunits (p301 or p302), and only 14 of the p2 or p30-specific clones reacted with TT presented by EBV-transformed B cell lines (B-LCL). The p30-specific clones were HLA-DP4 restricted. In contrast to autologous B cell lines, the majority of allogeneic, but HLA-DP4-positive cell lines failed to present p30 to the specific clones. We concluded that T cell clones are highly specific and that both, small alterations of the peptide length as well as discrete differences of the HLA-molecule may abrogate recognition of the peptide HLA complex by T cells. Moreover, use of peptides as stimulators of T cells may recruit and activate T cells which fail the "original" peptide, derived from normal antigen processing. Clones could usually be maintained in culture for 4-6 months, but with the help of freezing and thawing some clones are now available for over 2 years and still specific. Comparison of different autologous antigen-presenting cells, namely B-LCL and activated MHC class II-positive T cells revealed that not all clones were able to mount a proliferative response to peptide presentation by T cells, while all clones proliferated to B cells as APC. If stimulated with peptide and B-LCL, the clone proliferating to T cells as APC (so-called T responder clones) secreted a broad spectrum of cytokines (Th0-like) and were easier to maintain in culture. In contrast, clones which were unable to proliferate to peptide presentation, so-called T-nonresponder clones, showed a more restricted cytokine pattern and elevated or very low IL4/IFN gamma ratio upon antigen specific stimulation. However, all clones secreted at least small amounts of IL2, IL4, IFN gamma and TNF alpha, if stimulated by PMA and ionomycin. Thus, both chemical and antigen-specific stimulations should be considered if T cell clones are classified as Th1 or Th2, whereby those clones, which secrete a limited cytokine pattern after antigen stimulation only, might be named Th1 or Th2 like clones, while clones which even after PMA/ionomycin do not secrete all cytokines, might represent "real" Th1 or Th2 clones.