Background/Purpose:

T cells play a critical role in the body’s response to pathogens. A naïve T helper (Th0) cell proliferates in response to antigen encounter and is not differentiated. Specific cytokines signal the naive Th cell to express transcription factors causing differentiation to Th cell lineages, including Th1, Th2, and Th17 lines. Re-activation causes a differentiated effector Th cell to secrete characteristic cytokines, which are IFNγ, IL-5 and IL-13, and IL-17 for Th1, Th2, and Th17 cells respectively. In juvenile idiopathic arthritis (JIA), specific Th cell lineage differentiation and cytokine secretion have not been studied. An ex vivo assay was developed in adult human peripheral blood mononuclear cells (pBMCs) wherein mononuclear cells differentiate, re-activate, and then secrete cytokines. We identified a young child with JIA who has a heterozygous mutation in GATA-3, the key transcription factor that drives the Th2 pathway and suppresses the Th1 and Th17 pathways (index patient). In this study, we tested effector Th cell differentiation and cytokine secretion in pBMCs from young children, young children with JIA, and the index patient.

Methods: We enrolled healthy controls, children with seronegative polyarticular or extended oligoarticular JIA, and the index patient. All children were 2-8 years old. PBMCs underwent collection, ex vivo differentiation to Th0, Th1, Th2, and Th17 cells, and then re-stimulation. After this, cytokine secretion was measured by enzyme-linked immunosorbent assay. Transcription factor expression and cytokine transcription was assessed by Western blot and quantitative real time polymerase chain reaction. Whole exome sequencing identified the index patient GATA-3 mutation.

Results: Differentiated effector Th cell cultures from children with JIA secrete much higher levels of characteristic cytokines than healthy control children. The Th cell average JIA/control ratios were markedly increased for Th1 (IFNγ, 3.4), Th2 (IL-5, 6.0 and IL-13, 10.3), and Th17 (IL-17, 5.5). The index patient had increased index/control ratios for Th1 (IFNγ, 4.5) and Th17 (IL-17, 3.6) cultures and no change in Th-2 ratios. Surprisingly, the undifferentiated Th0 cells from children with JIA and the index patient secrete IFNγ, with ratios being JIA/control 5.5 and index/control 22.6. The ex vivo assay in healthy children produces much lower levels of cytokines than in healthy adults.

Conclusion: Young children produce differentiated effector Th cells that make much less cytokines than adult differentiated effector Th cells. Cultures from children with JIA make more cytokines than cultures from healthy children and are similar to adult cultures. The index patient does not produce differentiated Th2 cells that secrete IL-13 and IL-5, as might be predicted from a GATA-3 mutation. Both the JIA and index patient undifferentiated Th0 cell cultures secrete IFNγ, suggesting a Th1-like phenotype. Mechanisms underlying differences between effector Th cell cultures from young children, children with JIA, the index patient, and adults may reveal fundamental differences in these developmental processes, including limits on the function of the immune system in young children.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/effector-t-helper-cell-differentiation-and-cytokine-secretion-are-increased-in-young-children-with-juvenile-idiopathic-arthritis/