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- Blood Tfr or CXCR5+ Treg cells?
Fonseca et al. reported the existence of CD25+ “blood Tfr cells not fully licensed for suppressive function” (1). We and others recently reported that bona fide Tfr do not express CD25 (2-4). This raises the question of the nature of “follicular” cells found outside the follicles.
Blood Tfh-like cells have been described as cells able to promote differentiation and class switch recombination of naïve B cells (5). Not surprisingly given their location, they were found not to express Bcl6. These cells have been named (i) by their phenotype (human blood CXCR5+ T cells (6)), (ii) by their function (the counterpart of T follicular cells (7)), (iii) as “blood Tfh-like cells” (8) cells or more confidently as (iv) “blood Tfh cells” (9). These non-consensual naming denote some unease about qualifying cells with a localization descriptor (i.e. follicular) that does not match their actual localization. Actually, although CXCR5+Bcl6- T cells have a clear B cell helper function, they have not yet been formally traced to a Tfh lineage. Whether they are post- or pre-Tfh cells or independent remains to be demonstrated.
The situation is even more complicated with “blood Tfr” cells, also named “Tfr-phenotype cells in peripheral blood” (10). While “blood Tfh” have a clear B cell helper function in vitro, “blood Tfr” “do not preferentially suppress [the] humoral response” in vitro (1).
As there are no lineage data supporting the concept of “blood Tfr” and “blood Tfh”, w...
Show MoreCompeting Interests: None declared.