Visualization and functional characterization of T-T cell interactions in vivo

To define the T-T cell interactions during differentiation of naïve CD4+ T helper cells in vivo displaying the interactions of naïve CD4+ and differentiated type 2 (TH2) T helper cells by measuring specific T helper (TH) cytokines. The homing capacity of naïve T cells bearing a T cell receptor (TCR) specific for influenza hemagglutinin (HA) or TH2 cells bearing a TCR specific for ovalbumin (OVA) was analyzed in draining lymph nodes of naïve murine BALB/c recipients after immunization and peptide challenge in vivo. T cell homing was visualized by flow cytometry (FACS) and fluorescence microscopy. For measuring different T cell specific cytokines we used established systems as Enzyme-Linked-Immunosorbent Assay (ELISA) and Enzyme-Linked-Immunospot-(ELISPOT) Assay for interferon(IFN)-γ and CT.4S assay and ELISPOT for IL-4 analysis. We showed that naïve and TH2 cells migrate with similar dynamics into draining lymph nodes and were found in close vicinity in T cell areas, when driven by antigen in complete Freunds’ adjuvant (CFA). Under these conditions, TH2 cells prevented CFA-mediated TH1-induction and deviated the differentiation of naïve TH cells toward a TH2 phenotype. OVA- TH2 cells induced TH2-differentiation in naïve T cells exclusively, if naïve and TH2 memory cells were both activated simultaneously in the same lymph node. ‘TH2’-cells from IL-4-/- mice were unable to affect CFA-mediated TH1-induction showing that TH2-derived IL-4 was strictly required to deviate naïve HA TH cells toward a TH2 phenotype. Among the various signals capable of promoting TH2 differentiation IL-4 is one of the most important factor for differentiation of naïve T cells into TH2 phenotype. Direct, IL-4-mediated, T-T cell interactions could be measured and demonstrated that TH2 derived IL-4 under restricted conditions plays a major role in TH cell differentiation in vivo.