Revealing the in vivo behavior of CD4+ T cells specific for an antigen expressed in Escherichia coli.

The clonal expansion and anatomic location of microbe-specific CD4+ Th cells was studied by tracking the fate of adoptively transferred DO11.10 TCR transgenic T cells specific for OVA peptide 323-339/I-Ad in BALB/c mice infected s.c. with Escherichia coli expressing a MalE-OVA fusion protein. After infection, the DO11.10 T cells accumulated in the T cell-rich paracortical regions of the draining lymph nodes, proliferated there for several days, and then moved into the B cell-rich follicles before they slowly disappeared from the lymph nodes. These changes occurred despite the fact that viable organisms were never found in the lymph nodes. The DO11.10 T cells also accumulated in the s.c. infection site, but about 1 day later than in the draining lymph nodes. Injection of purified MalE-OVA fusion protein alone induced a transient accumulation of DO11.10 T cells in the paracortical regions, but these T cells never entered follicles and the mice did not produce anti-OVA antibodies. The DO11.10 T cells that survived in animals injected with MalE-OVA alone were hyporesponsive to in vitro Ag restimulation and did not produce IL-2 and IFN-gamma, whereas DO11.10 T cells from mice infected with MalE-OVA-expressing bacteria produced both lymphokines. These results suggest that Ag-specific T cells are first activated in secondary lymphoid organs following primary bacterial infection and then migrate to the infection site. Furthermore, productive activation of the T cells during the primary response is dependent on bacterial components other than the Ag itself.