Helios Is Associated with CD4 T Cells Differentiating to T Helper 2 and Follicular Helper T Cells In Vivo Independently of Foxp3 Expression

Abstract

BackgroundAlthough in vitro IL-4 directs CD4 T cells to produce T helper 2 (Th2)-cytokines, these cytokines can be induced in vivo in the absence of IL-4-signalling. Thus, mechanism(s), different from the in vitro pathway for Th2-induction, contribute to in vivo Th2-differentiation. The pathway for in vivo IL-4-independent Th2-differentiation has yet to be characterized.FindingsHelios (ikzf2), a member of the Ikaros transcription regulator family, is expressed in thymocytes and some antigen-matured T cells as well as in regulatory T cells. It has been proposed that Helios is a specific marker for thymus-derived regulatory T cells. Here, we show that mouse ovalbumin-specific CD4 (OTII) cells responding to alum-precipitated ovalbumin (alumOVA) upregulate Th2 features - GATA-3 and IL-4 - as well as Helios mRNA and protein. Helios is also upregulated in follicular helper T (TFh) cells in this response. By contrast, OTII cells responding to the Th1 antigen - live attenuated ovalbumin-expressing Salmonella - upregulate Th1 features - T-bet and IFN-γ - but not Helios. In addition, CD4 T cells induced to produce Th2 cytokines in vitro do not express Helios. The kinetics of Helios mRNA and protein induction mirrors that of GATA-3. The induction of IL-4, IL-13 and CXCR5 by alumOVA requires NF-κB1 and this is also needed for Helios upregulation. Importantly, Helios is induced in Th2 and TFh cells without parallel upregulation of Foxp3. These findings suggested a key role for Helios in Th2 and TFh development in response to alum-protein vaccines. We tested this possibility using Helios-deficient OTII cells and found this deficiency had no discernable impact on Th2 and TFh differentiation in response to alumOVA.ConclusionsHelios is selectively upregulated in CD4 T cells during Th2 and TFh responses to alum-protein vaccines in vivo, but the functional significance of this upregulation remains uncertain.

Mechanism of Immunopotentiation and Safety of Aluminum Adjuvants

“…The ability of aluminum adjuvants to induce a Th2-biased immune response is the basis of the common use of these adjuvants in the induction of allergic diseases in mouse models. More recent studies showed that injection of mice with alum-precipitated protein induced a marked increase of antigen-specific T FH cells in the draining lymph nodes (Serre et al, 2011a,b). Comparison of T FH and non-T FH CD4 T cells suggested that T FH cells rather than Th2 cells were the major subpopulation of IL-4-secreting CD4 T cells (Serre et al, 2011a).…”

“…More recent studies showed that injection of mice with alum-precipitated protein induced a marked increase of antigen-specific T FH cells in the draining lymph nodes (Serre et al, 2011a,b). Comparison of T FH and non-T FH CD4 T cells suggested that T FH cells rather than Th2 cells were the major subpopulation of IL-4-secreting CD4 T cells (Serre et al, 2011a). Taken together these older and more recent studies suggest that aluminum adjuvants induce the differentiation of Th2 cells that drive an eosinophilic inflammatory response and T FH cells that stimulate antibody production.…”

The role of all-trans retinoic acid in the biology of Foxp3+ regulatory T cells

“…27 Similarly, Helios provides an additional marker for the discrimination of nTreg cells from iTreg cells, although its specificity remains a concern. 28,29 Nrp-1 also identifies Foxp3 1 cell stability because Nrp-1 1 nTreg cells are more stable compared with Nrp-1 2 nTreg cells. Nrp-1 1 nTreg cells have lower methylation levels in the Treg cell-specific demethylated region.…”

Treg Cells, Life History, and Diversity

“…It was suggested that expression of the transcription factor Helios (Ikzf2) might serve as a marker of thymus-derived Tregs (Thornton et al 2010). Unfortunately, it is now realized that Helios is expressed at substantial levels in pTregs induced peripherally by lymphopenia or agonist peptide (Verhagen and Wraith 2010;Darce et al 2012;Gottschalk et al 2012) and is generically induced upon activation of CD4 þ T cells (Akimova et al 2011;Serre et al 2011). Analyses of TCR repertoires in unchallenged mice have shown a high degree of similarity between Tregs in the thymus and peripheral lymphoid organs (Hsieh et al 2006;Pacholczyk et al 2006;Wong et al 2007b), suggesting that tTregs constitute the majority of those pools (there is admittedly a caveat to this argument, which assumes that there is little or no colonization of thymic pools by recirculation from the periphery).…”