Fig 7. Icos deficiency restricts T_CM cells from producing Tfh effector cells after reactivation.

(A) Experimental model. WT and Icos^-/- CD45.1⁺ mice were infected with 10⁵ P. c. chabaudi pRBCs and given CQ beginning at day 35 p.i. T_CM cells were sorted from WT and Icos^-/- CD45.1⁺ mice on day 90. 50–100,000 cells of each T_CM cell population were transferred retro-orbitally into separate CD45.2⁺ tcrb^-/- mice. WT CD45.2⁺ and tcrb^-/- mice that did not receive donor cells served as controls. Twenty-four hours later, half the mice were infected with 10⁵ P. c. chabaudi pRBCs. Mice were sacrificed at day 21 p.i. (B) Total number of live CD45.1⁺ CD4⁺ T cells recovered on day 21 p.i. (day 22 post-transfer). (C) Representative plots of CXCR5 and PD-1 expression on live activated (CD44^hiCD62L^lo) CD45.1⁺ CD4⁺ T cells at day 21 p.i. Upper gates indicated GC Tfh (CXCR5⁺PD-1⁺⁺) cells, and lower gates represent Tfh-like (CXCR5⁺PD-1⁺) cells. The total number of live activated CD45.1⁺ CD4⁺ (D) GC Tfh and (E) Tfh-like cells. Data are pooled from two independent experiments with at least three mice per group (error bars, s.e.m.). Significance calculated by one-way ANOVA Kruskal-Wallis test with post hoc Dunn’s multiple comparisons test. ** p < 0.01, **** p < 0.0001, NS not significant.