Identification of Human B-1 Helper T Cells With a Th1-Like Memory Phenotype and High Integrin CD49d Expression
- Jae-Ghi Lee,1 Joon Young Jang,1 Taishi Fang,1 Yixuan Xu,1 Ji-Jing Yan,1 Jung-Hwa Ryu,2 Hee Jung Jeon,3 Tai Yeon Koo,1 Dong Ki Kim,4 Kook-Hwan Oh,4 Tae Jin Kim,5,* and Jaeseok Yang1,2,6,*
- Front Immunol 2018; 9:1617
Human B-1 cells have been proposed to be CD20+CD27+CD43+CD1c- B cells found in the umbilical cord and adult peripheral blood, but their regulatory mechanisms have not been well elucidated. Previously, we reported that mouse CD49dhighCD4+ T cells could enhance the secretion of natural antibodies by B-1 cells (J Immunol 2015; 195(2):564-75). In this study, we aimed to investigate the presence and helper functions of the human equivalents of murine CD49dhighCD4+ T cells. Here, we showed that human CD49dhighCD4+ T cells found in the peritoneal cavity (PEC), spleen, and peripheral blood can enhance the production of IgM antibodies by B-1 cells. As revealed in mouse, CD49dhighCD4+ T cells were more abundant in the PEC and showed a higher tendency to form conjugates with B cells than CD49dlowCD4+ T cells. Moreover, CD49dhighCD4+ T cells showed a Th1-like memory phenotype, characterized by high expression of CD44 and CXCR3; low expression of CD62L and CCR7; rapid production of IFN-γ, tumor necrosis factor-α, and IL-2 upon stimulation with phorbol myristate acetate and ionomycin; and rapid proliferation upon stimulation with anti-CD3 and anti-CD28 antibodies. These cells also expressed high levels of PD-1, ICOS, and CD5, suggesting that they are undergoing chronic stimulation. Remarkably, CD49dhighCD4+ T cells specifically helped B-1 cells, but not follicular memory B cells (CD27+CD43-CD1c-) or marginal zone B cells (CD27+CD43-CD1c+), produce IgM and IgG antibodies. In parllel, the titer of human anti-blood group A IgM was positively correlated with the frequency of CD49dhighCD4+ T cells. In conclusion, we identified human CD49dhighCD4+ T cells with a Th1-like memory phenotype that secrete Th1 proinflammatory cytokines and help B-1 cells secrete antibodies, thereby aiding in primary defense. We suggest that these CD49dhighCD4+ T cells are a unique type of B-cell helper T cells distinct from follicular helper T cells.
This study is in collaboration with Prof. Yang’s laboratory at Seoul National University Hospital Transplantation Research Institute. The requirement of helper T cells in the B cell high affinity antibody response have been well appreciated for a long time. In contrast, B-1 cells, an evolutionally old type of B cells, have previously been known to produce natural antibodies independently of helper T cells. With respective 2015 and 2018 articles about mouse and human B-1 helper T cells, we showed that B-1 cell antibody response could be enhanced by a special type of B-1 helper T cells although B-1 cell antibody response could still occur in the absence of helper T cells. The integrin expression characteristics were also identical in mouse and human B-1 helper T cells (Immune Netw 2017; 17(6):392-401). Therefore, the role of helper T cells in the B cell antibody responses should be re-addressed as we suggest in the Figure 1. Figure 2 and 3 show critical data showing the identification of B-1 helper T cells and their function.
Figure 1. The sub-classification of the T cell-dependent (TD) Ab responses. In the left panel (depicted as TD-3 response), a B cell is activated by an innate stimulus (not depicted, a TI response) and/or an innate-like T cell through non-cognate interaction involving T cell receptors (TCRs) and antigen-presenting molecules, such as major histocompatibility complex (MHC) or CD1d (not depicted), irrespective of the B cell receptor (BCR) specificity (TD-3 response). The activated B cell can proliferate and advance further to interact with other T cells, eventually resulting in a cognate interaction involving TCRs and peptides derived from BCR-bound proteins. This interaction may lead to an extrafollicular Ab response (TD-2 response, right upper) or eventual germinal center (GC) formation (TD-1 response, right lower). iNKT cell can provide cognate help for MZ B cells, leading to extrafollicular MZ B cell response as shown in right upper corner.
Figure 2. CD49dhighCD4+ T cells were more prevalent in the human peritoneal cavity than in the spleen or peripheral blood. Flow cytometric plots show the expression of CD4 and CD49d (integrin α4) in cells from given compartments.
Figure 3. CD49dhighCD4+ T cells help immunoglobulin secretion by human B-1 cells. Sorted peripheral blood-derived CD49dhighCD4+ T cells or CD49dlowCD4+ T cells were co-cultured with sorted naïve (CD20+CD27−CD43−CD1c−), memory (CD20+CD27+ CD43−CD1c−), marginal zone (CD20+CD27+CD43−CD1c+), and B-1 (CD20+ CD27+CD43+CD1c−) B cells for 5 days in the presence of immobilized anti-CD3 antibody. Concentrations of human IgM and IgG in the culture supernatant were compared among the B cell alone group (gray), the CD49dhighCD4+ T cell group (black), and the CD49dlowCD4+ T cell group (white). Data are expressed as the mean ± SEM (n = 3–5 donors per each group). *P < 0.05, **P < 0.01; Student’s t-test. Abbreviations: PEC, peritoneal cavity; SP, spleen; PB, peripheral blood.