Table 1.

Cellular players in immune tolerance in allergy and cancer.

Section	Cell type	Proposed roles in allergy	Proposed functions in cancer
3.1	Dendritic cells	Support conversion of T cells into Tregs	Depending on differentiation; Support conversion of T cells into immunosuppressive Tregs, promoting cancer progression
3.2	Macrophages	M2a macrophages support allergic diseases M2b have immunoregulatory functions	Depending on subtype; M1 macrophages support survival Low M1/M2 ratios associated with poor survival M2b associated with tolerogenic tumour microenvironment
3.3	Tregs	Source of IL-10, supported by IL-10 Foster IgG4 production and suppress allergies	Accumulate in cancer tissue Correlate with disease progression
3.4	Bregs	Source and recipient of IL-10 Origin of IgG4 in allergen immunotherapy	Source and recipient of IL-10 Origin of IgG4 in cancer tissues, where they correlate with disease severity and poorer outcomes
3.5	Innate lymphoid cells (ILCs)	Source of Th2 cytokines and thus involved in initiation of allergy	Depending on subtype; ILC2 may in a tumour provide an immunosuppressive environment, like ILC3s which support IL-10 secretion
3.6	Mast cells	Major effector cells in allergy and source of IL-4	Controversial; Can engender pro- or anti-tumoural functions, depending on micro-localization and type of tumour A source of TNFα; Can express PD-L1 or -L2 and inhibit effector T cells.
3.7	Eosinophils	Involved in chronic allergic and atopic conditions and associated with curative processes	Controversial; Attracted by CCL1 in tumour; Can be pro- (Hodgkin´s lymphoma) or anti-tumorigenic (in solid tumours); May sense tumour cells in innate manner and kill in concert with Igs; May induce Tregs
3.8	Epithelial cells	Contribute to site-specific tolerance induction, mainly via DC interactions; Epithelial barrier disruption stimulates allergen entry and epithelial activation; Source of TSLP and IL-33, supporting Th2 responses	Source of immunosuppressive microvesicles, with a potential role in cancer promotion