Pathogenic CD4 + T cells regulating B‐cell differentiation in autoimmunity: not exactly Tfh cells

Occurrence and role of Tph cells in various renal diseases

A new population of peripheral helper T (Tph) cells has been identified and contributed to various autoimmune diseases. Tph cells can secrete interleukin-21 (IL-21), interferon (IFN) and C-X-C motif chemokine ligand 13 (CXCL13) to moderate renal disease. Moreover, Tph cells can congregate in huge numbers and immerse within inflamed tissue. Compared to Tfh cells, Tph cells express high programmed cell death protein 1 (PD-1), major histocompatibility complex II (MHC-II), C-C chemokine receptor 2 (CCR2) and C-C chemokine receptor 5 (CCR5) but often lack expression of the chemokine receptor C-X-C chemokine receptor 5 (CXCR5). They display features distinct from other T cells, which are uniquely poised to promote responses and antibody production of B cells within pathologically inflamed non-lymphoid tissues and a key feature of Tph cells. In this review, we summarize recent findings on the role of Tph cells in chronic kidney disease, acute kidney injury, kidney transplantation and various renal diseases.

Altered peripheral helper T cells in peripheral blood and muscle tissue of the patients with dermatomyositis

Peripheral helper T (Tph) cells, phenotypically PD-1hiCXCR5-CD4+, are a recently identified Th cell subset that relates to several autoimmune diseases. Contrary to PD-1hiCXCR5+CD4+ follicular helper T (Tfh) cells, Tph cells are not located in lymphoid organs but accumulate in inflamed tissues. This study investigated Tph cells to determine their involvement in dermatomyositis (DM). The frequency of circulating Tph and Tfh cells was evaluated by flow cytometry at baseline and after glucocorticoid treatment. The expression of Tph and B cells was determined in muscle tissue by immunohistochemistry (IHC). Further, the correlations between circulating Tph cells and clinical characteristics were investigated. Flow cytometry revealed that circulating Tph and Tfh cells were decreased in peripheral blood of DM patients compared with healthy controls (HCs). However, the muscular expression of Tph and B cells was upregulated in patients with DM compared to that in the controls by IHC. Interestingly, the increased B cells accumulated around Tph cells in infiltrated lesions. The frequency of circulating Tph cells was positively correlated with Tfh cells, CD3+ T cells, CD4+ T cells, and CD8+ T cells, whereas negatively correlated with erythrocyte sedimentation rate (ESR), interleukin (IL)-6, and IL-10 levels. Furthermore, the abnormal circulating Tph cells in peripheral blood were recovered after glucocorticoid treatment. These results indicate that Tph cells might be involved in the immunopathogenesis of DM and therefore might provide novel insight for the development of DM therapies.

Two populations of circulating PD-1hiCD4 T cells with distinct B cell helping capacity are elevated in early rheumatoid arthritis

Objective

A novel population of B helper cells, phenotypically CD4+CXCR5−PD-1hi, has been described in the synovial tissues and peripheral blood of seropositive RA patients, and termed ‘peripheral helper T’ (Tph) cells. Contrary to CD4+CXCR5+PD-1hi follicular helper T (Tfh), Tph cells are not located in lymphoid organs but accumulate in inflamed tissues. Our objective was to study the frequency of circulating Tph (cTph) and circulating Tfh cell counterparts (cTfh) in patients with early RA (eRA).

Methods

Freshly isolated peripheral blood mononuclear cells from 56 DMARD-naïve eRA patients and 56 healthy controls were examined by flow cytometry. Autologous cocultures of naïve or memory B cells were established with isolated peripheral blood Tph or Tfh cells.

Results

Seropositive (RF+ and/or ACPA+, n = 38) but not seronegative eRA patients (n = 18) demonstrated increased frequencies and absolute numbers of cTph and cTfh cells. cTph but not cTfh cells expressed CCR2. Those eRA patients who experienced a significant clinical improvement at 12 months demonstrated a marked decrease of their cTph cell numbers whereas their cTfh cell numbers remained unchanged. Both isolated Tph and isolated Tfh cells were able to induce maturation of memory B cells, whereas only Tfh cells could differentiate naïve B cells.

Conclusion

Two populations of PD-1hiCD4 T cells with distinct phenotype and B cell helping capacity are increased in the peripheral blood of seropositive eRA patients. Whereas cTph cells are present only in patients with an active disease, cTfh cells seem to be constitutively elevated.

Tailoring Immune Responses toward Autoimmunity: Transcriptional Regulators That Drive the Creation and Collusion of Autoreactive Lymphocytes

T-dependent humoral immune responses to infection involve a collaboration between B and CD4 T cell activation, migration, and co-stimulation, thereby culminating in the formation of germinal centers (GCs) and eventual differentiation into memory cells and long-lived plasma cells (PCs). CD4 T cell-derived signals drive the formation of a tailored B cell response. Downstream of these signals are transcriptional regulators that are the critical enactors of immune cell programs. In particular, a core group of transcription factors regulate both B and T cell differentiation, identity, and function. The timing and expression levels of these transcription factors are tightly controlled, with dysregulated expression correlated to immune cell dysfunction in autoimmunity and lymphomagenesis. Recent studies have significantly advanced our understanding of both extrinsic and intrinsic regulators of autoreactive B cells and antibody-secreting PCs in systemic lupus erythematosus, rheumatoid arthritis, and other autoimmune conditions. Yet, there are still gaps in our understanding of the causative role these regulators play, as well as the link between lymphoid responses and peripheral damage. This review will focus on the genesis of immunopathogenic CD4 helper and GC B cells. In particular, we will detail the transcriptional regulation of cytokine and chemokine receptor signaling during the pathogenesis of GC-derived autoimmune conditions in both murine models and human patients.