Serosal Cavities Contain Two Populations of Innate-like integrin α4highCD4+ T Cells, Integrin α4β1+α6β1+α4β7- and α4β1+α6β1-α4β7+ Cells

Screening of integrins localized on the surface of human epidermal melanocytes

In vivo, melanocytes occupy three-dimensional (3D) space. Nevertheless, most experiments involving melanocytes are performed in a two-dimensional microenvironment, resulting in difficulty obtaining accurate results. Therefore, it is necessary to construct an artificial in vivo-like 3D microenvironment. Here, as a step towards engineering a precisely defined acellular 3D microenvironment supporting the maintenance of human epidermal melanocytes (HEMs), we examined the types of integrin heterodimers that are expressed transcriptionally, translationally, and functionally in HEMs. Real-time PCR and fluorescent immunoassay analyses were used to elucidate the expression of integrin α and β subunit genes at the transcriptional and translational levels, respectively. The functionality of the presumed integrin heterodimers was confirmed using attachment and antibody-inhibition assays. Among the genes encoding 12 integrin subunits (α₁, α₂, α₃, α₄, α₅, α₆, α₇, α_V, β₁, β₃, β₅, and β₈) showing significantly higher transcription levels, proteins translated from the integrin α₂, α₄, α₅, β₁, β₃, and β₅ subunit genes were detected on the surface of HEMs. These HEMs showed significantly increased adhesion to collagen I, fibronectin, laminin, and vitronectin, and functional blockade of the integrin α₂ subunits significantly inhibited adhesion to collagen I, fibronectin, and laminin. In addition, there was no significant inhibition of the adhesion to fibronectin or vitronectin in HEMs with functional blockade of the integrin α₄, α₅, or α_V subunits. These results indicate that the active integrin α₂β₁ heterodimer and the inactive integrin α₄, α₅, α_V, β₃, and β₅ subunits are all localized on the surface of HEMs.

Expansion and Sub-Classification of T Cell-Dependent Antibody Responses to Encompass the Role of Innate-Like T Cells in Antibody Responses

In addition to T cell-dependent (TD) Ab responses, T cells can also regulate T cell-independent (TI) B cell responses in the absence of a specific major histocompatibility complex (MHC) class II and antigenic peptide-based interaction between T and B cells. The elucidation of T cells capable of supporting TI Ab responses is important for understanding the cellular mechanism of different types of TI Ab responses. Natural killer T (NKT) cells represent 1 type of helper T cells involved in TI Ab responses and more candidate helper T cells responsible for TI Ab responses may also include γδ T cells and recently reported B-1 helper CD4⁺ T cells. Marginal zone (MZ) B and B-1 cells, 2 major innate-like B cell subsets considered to function independently of T cells, interact with innate-like T cells. Whereas MZ B and NKT cells interact mutually for a rapid response to blood-borne infection, peritoneal memory phenotype CD49d^highCD4⁺ T cells support natural Ab secretion by B-1 cells. Here the role of innate-like T cells in the so-called TI Ab response is discussed. To accommodate the involvement of T cells in the TI Ab responses, we suggest an expanded classification of TD Ab responses that incorporate cognate and non-cognate B cell help by innate-like T cells.

Identification of Human B-1 Helper T Cells With a Th1-Like Memory Phenotype and High Integrin CD49d Expression

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 CD49d^high CD4⁺ T cells could enhance the secretion of natural antibodies by B-1 cells. In this study, we aimed to investigate the presence and helper functions of the human equivalents of murine CD49d^high CD4⁺ T cells. Here, we showed that human CD49d^high CD4⁺ 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, CD49d^high CD4⁺ T cells were more abundant in the PEC and showed a higher tendency to form conjugates with B cells than CD49d^low CD4⁺ T cells. Moreover, CD49d^high CD4⁺ 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, CD49d^high CD4⁺ 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 parallel, the titer of human anti-blood group A IgM was positively correlated with the frequency of CD49d^high CD4⁺ T cells. In conclusion, we identified human CD49d^high CD4⁺ 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 CD49d^high CD4⁺ T cells are a unique type of B-cell helper T cells distinct from follicular helper T cells.