Figure 2.

Peripheral blood follicular T cells. These cells are distinguished from conventional CD4⁺ T cells by the expression of CXCR5 and helper subsets categorized based on chemokine receptor, programmed death 1 (PD)‐1 and inducible T cell co‐stimulator (ICOS) expression. (a) Examining forkhead box protein 3 (FoxP3) and CXCR5 expression on live, single‐cell, CD3⁺CD4⁺ T cells reveals four distinct subsets (clockwise from top left quadrant): CCXR5^–FoxP3⁺ regulatory T cells (T_reg); CXCR5⁺FoxP3⁺ follicular T helper (Tfr); CXCR5⁺FoxP3^– Tfh; and CXCR5^–FoxP3^– conventional T cells. The absence of CXCR5 fluorochrome‐conjugated antibody in T_reg analysis would result in Tfr being analysed simultaneously with conventional T_reg. Simultaneously, FoxP3 fluorochrome‐conjugated antibodies (or other regulatory markers) are required to distinguish between Tfh and follicular regulatory T (Tfr) cells. (b) CXCR5⁺FoxP3^–CD45RA^– Tfh cells can be categorized as Tfh17 (CCR6⁺CXCR3^–), Tfh17.1 (CCR6⁺CXCR3⁺), Tfh1 (CCR6^–CXCR3⁺) and Tfh2 (CCR6^–CXCR3^–). CCR4 and CD161 expression may be used to refine Tfh subsets further (refer to Table 1). (c) While helper capacity of Tfh1 cells is restricted to the activated ICOS⁺PD‐1⁺⁺CCR7^lo subset, all Tfh2 and Tfh17 cells are capable of helping B cells with varying capacity. The intensity of the background greyscale reflects the capacity to provide help to B cells. This figure has been adapted from reference 51 with permission from the authors.