“…Although T FH cells are predominantly located in the secondary lymphoid organs, circulating T FH cells can be identified in the blood. 13,14 Circulating T FH 13 cells can either be identified using nonspecific activation with PMA/ionomycin or specific activation with allergen. 9,15 While the latter has the advantage of resolving numbers of antigen-specific T FH 13 cells, this is only possible when the antigen is known.…”