Accessing Early Differentiation of Virus-Specific Follicular Helper CD4⁺ T Cell in Acute LCMV-Infected Mice

Follicular Helper T (T_FH) cells are perceived as an independent CD4⁺ T cell lineage that assists cognate B cells in producing high-affinity antibodies, thus establishing long-term humoral immunity. During acute viral infection, the fate commitment of virus-specific T_FH cells is determined in the early infection phase, and investigations of the early-differentiated T_FH cells are crucial in understanding T cell-dependent humoral immunity and optimizing vaccine design. In the study, using a mouse model of acute lymphocytic choriomeningitis virus (LCMV) infection and the TCR-transgenic SMARTA (SM) mouse with CD4⁺ T cells specifically recognizing LCMV glycoprotein epitope I-A^bGP_66-77, we described procedures to access the early fate commitment of virus-specific T_FH cells based on flow cytometry stainings. Furthermore, by exploiting retroviral transduction of SM CD4⁺ T cells, methods to manipulate gene expression in early-differentiated virus-specific T_FH cells are also provided. Hence, these methods will help in studies exploring the mechanism(s) underlying the early commitment of virus-specific T_FH cells.