Coordination between T helper cells, iNKT cells, and their follicular helper subsets in the humoral immune response against Clostridium difficile toxin B

Abstract

Activation of iNKT cells with the CD1d-binding glycolipid adjuvant α-galactosylceramide (α-GC) enhances humoral immunity specific for coadministered T-dependent Ag. However, the relationship between the iNKT cell and the classic T helper (Th) or T follicular helper (Tfh) function following this immunization modality remains unclear. We show that immunization with the C-terminal domain (CTD) of Clostridium difficile toxin B (TcdB), accompanied by activation of iNKT cells with α-GC, led to enhanced production of CTD-specific IgG, which was CD1d- and iNKT cell-dependent and associated with increased neutralization of active TcdB. Immunization with CTD plus α-GC followed by NP hapten-linked CTD increased NP-specific IgG1 titers in an NKT-dependent manner, suggesting that iNKT activation could enhance Th or Tfh function or that iNKT and iNKTfh cells could provide supplemental, yet independent, B cell help. Th, Tfh, iNKT, and iNKTfh cells were, therefore, examined quantitatively, phenotypically, and functionally following immunization with CTD or with CTD plus α-GC. Our results demonstrated that α-GC-activated iNKT cells had no direct effect on the numbers, phenotype, or function of Th or Tfh cells. However, CD4 T cell-specific ablation of the Bcl6 transcription factor demonstrated that Tfh and iNKTfh cells both contributed to B cell help. This work extends our understanding of the immune response to vaccination and demonstrates an important contribution by NKTfh cells to humoral immunity.

Insights Into the Molecular Mechanisms of T Follicular Helper-Mediated Immunity and Pathology

“…Similar to the development of conventional Tfh cells, the formation of NKTfh cells is dependent on CD28-mediated cognate interactions with B cells and Bcl6 expression ( 196 ). Studies utilizing CD4 + T cell-specific loss of Bcl6 determined that both Tfh and iNKTfh cells contribute to B cell help ( 197 ). However, unlike Tfh-derived B cell responses, those driven by NKTfh cells have no potential to generate long-lived plasma cells and memory B cells ( 196 ).…”

Activation and Regulation of B Cell Responses by Invariant Natural Killer T Cells

“…Stimulation of iNKT cells isolated from the pleural fluid of humans with tuberculosis with Mycobacterium tuberculosis antigens results in their expression of CXCR5, release of IL-21 and the provision of cognate B cell help for the production of IgG and IgA ( 64 ). Both T FH and iNKT FH cells contribute to B cell help and the production of antibodies to Clostridium difficile toxin B in mice ( 65 ). Furthermore, CD1d expression by B cells was required for iNKT cell-mediated B cell help to a protein antigen in mice co-immunized with a mixture of the protein antigen and α-GalCer, indicating that cognate iNKT cell–B cell interactions can play a role in the development of antibody responses to protein antigens ( 53 ).…”

The Influence of Invariant Natural Killer T Cells on Humoral Immunity to T-Dependent and -Independent Antigens

“…Fewer studies have addressed whether there is direct communication between Th/Tfh and NKT/NKT follicular helper cells (NKTfh) cells during a humoral response. Our studies showed a temporal relationship between Th/Tfh and NKT/NKTfh production of IL-4 and IL-21, with the NKT/NKTfh compartments providing an early source of IL-21 ( 27 ). However, we did not detect any direct dependence of one cell type upon the other with regard to cytokine secretion.…”

“…This phenomenon explains the previous identification of an IL-21-secreting NKT subset ( 59 ), which is now known to express high levels of the master transcriptional regulator Bcl6, and upregulate the chemokine receptor CXCR5, and the PD1 molecule. The NKT subset may provide an early source of IL-21 ( 27 ) and perhaps accelerate Ig class switch, an effect that may have been missed in earlier studies examining cytokine contributions ( 3 ). The NKT-enhanced IgG response to T-dependent Ag is typically IgG1-dominated and this makes sense given the pivotal role of Tfh-derived IL-21 in IgG1 class switch ( 60 , 61 ).…”