Figure 3.

The recovery of CD4 T cells after sepsis involves antigen-dependent and independent pathways. The “coloring” of T cells depicted in the top of the illustration represents different antigen-specific populations, amongst a representation of the peripheral CD4 T-cell mass. Sepsis causes a stochastic loss of CD4 T cells by apoptosis, and the end result for a significant group of patients is a state of lymphopenia that is most pronounced for certain cell populations (one such lymphocyte being CD4 T cells). After sepsis, however, a bulk number of peripheral CD4 T cells returns to baseline. Despite the numerical recovery of peripheral CD4 T cells, the diversity and size of Ag-specific CD4 T cell populations change after sepsis. The bottom square “zooms in” in some of the changes occurring to specific CD4 T-cell populations during sepsis that make it possible for antigenic diversity to change. These include both Ag-dependent and independent pathways of recovery. Ag-independent changes in T-cell recovery is mediated mostly by homeostatic proliferation, whereas Ag-dependent changes in T-cell repertoire distribution are influenced by (mostly) cross-reactivity to Ag sampled from the host microbiome.