The Expansion in Lymphoid Organs of IL-4⁺BATF⁺ TFH Cells is Linked to IgG4 Class Switching in vivo

Objectives: Distinct T follicular helper (TFH) subsets that influence specific class-switching events are assumed to exist, but the accumulation of isotype-specific TFH subsets in human secondary lymphoid organs (SLOs) and tertiary lymphoid organs (TLOs) has not been hitherto demonstrated. IgG4-related disease (IgG4-RD) is a chronic, systemic, inflammatory condition with polarized class-switching to IgG4 and frequent hyperplastic germinal center (GC) formation. TFH cells generally contribute to isotype-switching and GC formation in T-dependent immune responses. We sought to determine the frequency of distinct TFH cells that express IL-4 in the SLOs and TLOs of IgG4-RD and control subjects.
Methods: Multi-color immunofluorescence and flow cytometry was used to examine distinct TFH cells and B cells in normal SLOs from control subjects and from SLOs and TLOs of subjects with IgG4-RD and Sjögren’s syndrome (SS). Isolating TFH cell subsets based on cytokine, gene expression and surface marker profiles can help us gain better insights into the biology of specific TFH subsets. We therefore use an transcriptomes of IL-4 secreting TFH cells differ both from PD-1^hiTFH cells that do not secrete IL-4 and IL-4-secreting non-TFH cells, by using an IL-4-capture assay followed by FACS sorting.
Results: IL-4⁺ TFH cells are surprisingly sparse in human SLOs. In sharp contrast, in IgG4-RD, a disorder characterized by polarized Ig class switching, most TFH cells in TLOs and SLOs make IL-4. Human IL-4⁺TFH cells do not express GATA-3 but express nuclear BATF, and the transcriptomes of IL-4 secreting TFH cells differ both from PD1^hiTFH cells that do not secrete IL-4 and IL4-secreting non-TFH cells (TH2). These IL-4⁺TFH cells, express BATF, ICOS, and CD40L, and can be detected in cell-cell contact with IgG4⁺B cells, some of these cells express AID. Unlike IgG4-RD, IL-4⁺TFH cells are rarely found in TLOs in SS, a disorder in which IgG4 is not elevated. The proportion of CD4⁺IL-4⁺BATF⁺TFH cells as well as of CD4⁺IL-4⁺CXCR5⁺TFH cells in IgG4-RD tissues correlates tightly with tissue IgG4 plasma cell numbers and plasma IgG4 levels in patients but not with the total plasma levels of other isotypes.
Conclusions: These data describe a disease-related TFH sub-population in human TLOs and SLOs that is linked to IgG4 class switching (Image).