Figure 10. Models of CD8+ T cell function during chronic reactivating brucellosis.

A) Model of CD8+ T cell functional response during chronic infection with Brucella melitensis. Initially, CD8+ T cells respond to B. melitensis and clonally expand with many clones producing one cytokine such as IFNγ, while fewer clones produce two or three cytokines. With continuing waves of Brucella release from infected cells, CD8+ T cell expansion is reduced with fewer and fewer cells producing multiple cytokines and a larger pool of cells producing no detectable cytokines representing an exhausted phenotype. Adapted from [87]. B) Model of CD8+ T cell expression of individual cytokines. Black dotted line represents background level of expression in uninfected mice. As waves of Brucella are released from infected cells, cytokine expression occurs with reduction of IFNγ and no IL-2 or TNFα expression.