A subset of AID-dependent B-1a cells initiates hypersensitivity and pneumococcal pneumonia resistance.

We propose that there is a special B-1a B cell subset ("sB-1a" cells) that mediates linked processes very early after immunization to initiate cutaneous contact sensitivity (CS), delayed-type hypersensitivity (DTH), and immune resistance to pneumococcal pneumonia. Our published data indicate that in CS and DTH, these initiating processes are required for elicitation of the delayed onset and late-occurring classical T cell-mediated responses. sB-1a cells resemble memory B2 cells, as they are stimulated within 1 h of immunization and depend on T helper cytokines-uniquely IL-4 from hepatic iNKT cells--for activation and rapid migration from the peritoneal cavity to the spleen to secrete IgM antibody (Ab) and Ab-derived free light chains (FLCs) by only 1 day after immunization. Unlike conventional B-1a (cB-1a) cell-produced IgM natural Ab, IgM Ab produced by sB-1a cells has high Ag affinity owing to immunoglobulin V-region mutations induced by activation-induced cytidine deaminase (AID). The dominant cB-1a cells are increased in immunized AID-deficient mice but do not mediate initiation, CS, or pneumonia resistance because natural Ab has relatively low Ag affinity because of unmutated germ-line V regions. In CS and DTH, sB-1a IgM Ag affinity is sufficiently high to mediate complement activation for generation of C5a that, together with vasoactive mediators such as TNF-α released by FLC-sensitized mast cells, activate local endothelium for extravascular recruitment of effector T cells. We conclude by discussing the possibility of functional sB-1 cells in humans.

Interleukin-5 plays a key role in mouse strain- dependent susceptibility to contact hypersensitivity through its effects on initiator B cells.

BACKGROUND: Elicitation of contact hypersensitivity requires antigen-specific immunoglobulin M (IgM) antibodies that trigger recruitment of effector T cells to the local tissue. These antigen-specific IgM antibodies are produced by B-1-like 'initiator B cells'. In this study, we compared susceptibility to hapten-induced contact hypersensitivity between BALB/c and C57BL/6 mice. METHODS: BALB/c and C57BL/6 mice were sensitized by painting oxazolone onto the skin and were challenged on the ears with the same hapten on day 4. Ear thickness and serum hapten-specific IgM levels were measured at 24 h post-challenge. Peritoneal cells were harvested and the numbers of B cell subpopulations were counted. Interleukin (IL)-5 was intraperitoneally injected into BALB/c and C57BL/6 mice, and the change in numbers of B cell subpopulations and serum IgM levels was monitored. RESULTS: Oxazolone induced stronger ear swelling and specific IgM responses in BALB/c mice than in C57BL/6 mice. BALB/c mice had higher numbers of peritoneal B-1 cells than C57BL/6 mice at steady state. IL-5 injection increased the number of peritoneal B-1 cells and serum IgM levels more significantly in BALB/ mice than in C57BL/6 mice. CONCLUSIONS: BALB/c mice exhibit higher susceptibility to hapten-induced contact hypersensitivity than C57BL/6 mice, most likely because they have a higher number of B-1 cells, leading to massive production of hapten-specific IgM antibodies upon contact sensitization. The differences in the number of B-1 cells and IgM responses between the two strains of mice may be attributed to the difference in responsiveness of B-1 cells to IL-5.

Identification of innate IL-5-producing cells and their role in lung eosinophil regulation and antitumor immunity.

IL-5 is involved in a number of immune responses such as helminth infection and allergy. IL-5 also plays roles in innate immunity by maintaining B-1 B cells and mucosal IgA production. However, the identity of IL-5-producing cells has not been unambiguously characterized. In this report, we describe the generation of an IL-5 reporter mouse and identify IL-5-producing non-T lymphoid cells that reside in the intestine, peritoneal cavity, and lungs in naive mice. They share many characteristics with natural helper cells, nuocytes, and Ih2 cells, including surface Ags and responsiveness to cytokines. However, these phenotypes do not completely overlap with any particular one of these cell types. Innate non-T IL-5-producing cells localized most abundantly in the lung and proliferated and upregulated IL-5 production in response to IL-25 and IL-33. IL-33 was more effective than IL-25. These cells contribute to maintaining sufficient numbers of lung eosinophils and are important for eosinophil recruitment mediated by IL-25 and IL-33. Given that eosinophils are shown to possess antitumor activity, we studied lung tumor metastasis and showed that innate IL-5-producing cells were increased in response to tumor invasion, and their regulation of eosinophils is critical to suppress tumor metastasis. Genetic blockade or neutralization of IL-5 impaired eosinophil recruitment into the lung and resulted in increased tumor metastasis. Conversely, exogenous IL-5 treatment resulted in suppressed tumor metastasis and augmented eosinophil infiltration. These newly identified innate IL-5-producing cells thus play a role in tumor surveillance through lung eosinophils and may contribute to development of novel immunotherapies for cancer.

Invariant NKT cells rapidly activated via immunization with diverse contact antigens collaborate in vitro with B-1 cells to initiate contact sensitivity.

In cutaneous contact sensitivity there is an early elicited innate cascade of complement, mast cells, and platelets activated via IgM Abs. This response is required to initiate the elicitation of acquired classical contact sensitivity by leading to local recruitment of effector T cells. We recently performed in vivo experiments showing that collaboration is required between innate-like invariant Valpha14+ NKT cells (iNKT) and the innate-like B-1 B cell subset to induce this initiation process. Contact sensitization triggers iNKT cells to produce IL-4 to coactivate the B-1 cells along with specific Ag for production of the initiating IgM Abs. We now describe in vitro collaboration of iNKT and B-1 cells. Normal peritoneal B-1 cells, incubated in vitro with soluble Ag, and with 1-h in vivo immune iNKT cells producing IL-4, are activated to mediate the contact sensitivity-initiation cascade. The three components of this process can be activated by different Ag. Thus, 1-h iNKT cell activation, B-1 cell stimulation, and generation of immune effector T cells can be induced by sensitization with three different Ag to respectively generate IL-4 and Ag-specific IgM Abs, to recruit the Ag-specific effector T cells. These findings have relevance to allergic and autoimmune diseases in which infections can trigger exacerbation of T cell responses to allergens or to autoantigens.

Interleukin 5 plays an essential role in elicitation of contact sensitivity through dual effects on eosinophils and B-1 cells.

BACKGROUND: Elicitation of contact sensitivity (CS) depends on B-1-cell-derived antigen-specific immunoglobulin M (IgM) antibodies that recruit CS effector T cells into the local tissue, which is followed by infiltration of antigen-nonspecific mononuclear cells and polymorphonuclear cells, such as neutrophils and eosinophils. In this study, we investigated the role of interleukin (IL)-5, which has broad effects on both eosinophils and B-1 cells, in elicitation of CS. METHODS: IL-5 receptor alpha-chain-deficient (IL-5Ralpha-/-) mice and IL-5Ralpha+/+ mice were contact sensitized with oxazolone hapten. Four days later, mice were challenged with the same hapten, and ear swelling responses were measured at 24 h after challenge. Eosinophil infiltration into the local tissue was determined by examination of skin histology and eosinophil peroxidase activity. To investigate the role of IL-5 in B-1 cell activation, the number of oxazolone-specific IgM-producing cells in the spleen was determined by enzyme-linked immunospot assay. RESULTS: Ear swelling responses in IL-5Ralpha-/- mice were about half of those in IL-5Ralpha+/+ mice, and nearly no eosinophil infiltration was observed in IL-5Ralpha-/- mouse skin. Eosinophil peroxidase activity in the sensitized and challenged IL-5Ralpha-/- mice was about 11 times less than that in immunized IL-5Ralpha+/+ mice. Contact sensitization significantly increased in numbers of oxazolne-specific IgM-producing cells in IL-5Ralpha+/+ mouse spleen, but not in IL-5Ralpha-/- mouse spleen. CONCLUSION: We conclude that IL-5-dependent activation of eosinophils and B-1 cells is necessary for induction and elicitation of CS. These findings provide a new insight into complicated mechanisms of CS elicitation and suggest a novel role of IL-5 in the regulation of immune responses.

Interleukin-4-dependent innate collaboration between iNKT cells and B-1 B cells controls adaptative contact sensitivity.

We showed that hepatic Valpha14+ invariant natural killer T (iNKT) cells, via their rapid interleukin (IL)-4 production, activate B-1 cells to initiate contact sensitivity (CS). This innate collaboration was absent in IL-4(-/-) and signal transducer and activator of transcription (STAT)-6(-/-) mice and was inhibited by anti-IL-4 treatment. These mice have defective CS because they fail to locally recruit the sensitized effector T cells of acquired immunity. Their CS is reconstituted by transfer of downstream-acting 1-day immune B-1 cells from wild-type mice. Responses were not reconstituted with B-1 cells from IL-4 receptor-alpha(-/-) or STAT-6(-/-) mice, nor by IL-4 treatment of B cell-deficient mice at immunization. Finally, IL-4 was preferentially and transiently produced by hepatic iNKT cells within 7 min after sensitization to mediate collaboration between innate-like iNKT cells and the B-1 B cells that participate in the recruitment of effector T cells in vivo.

TLR-dependent IL-4 production by invariant Valpha14+Jalpha18+ NKT cells to initiate contact sensitivity in vivo.

LPS stimulated B-1 cell polyclonal in vivo IgM responses depend on IL-4 release by invariant Valpha14+Jalpha18+ NKT (iNKT) cells. The IgM Abs can recruit effector T cells to mediate contact sensitivity. LPS activates the B-1 cell response just 1 day later, and depends on CD1d, iNKT cells, IL-4, TLR4, and MyD88. LPS in vivo and in vitro stimulates rapid preferential production of IL-4 in hepatic iNKT cells within 2 h. TLR4 were demonstrated in iNKT cells by flow cytometry and functional studies. Thus, innate microbial stimulation via TLR can activate iNKT cell and B-1 cell collaboration. The result is polyclonal IgM Ab responses capable of recruiting Ag-specific T cells into tissues. This may be involved in the promotion of autoimmunity by infectious agents.

An hour after immunization peritoneal B-1 cells are activated to migrate to lymphoid organs where within 1 day they produce IgM antibodies that initiate elicitation of contact sensitivity.

Elicitation of contact sensitivity (CS), a classic example of T cell-mediated immunity, requires Ag-specific IgM Abs to trigger an initiation process. This early process leads to local recruitment of CS-effector T cells after secondary Ag challenge. These Abs are produced by the B-1 subset of B cells within 1 day after primary skin immunization. In this study we report the surprising observation that B-1 cells in the peritoneal cavity are activated as early as 1 h after naive mice are painted with a contact-sensitizing Ag on the skin of the trunk and feet to begin the initiation of CS. B-1 cells in the spleen and draining lymph nodes produce the initiating Abs by 1 day after immunization, when we found increased numbers of Ag-specific IgM Ab-producing cells in these tissues by ELISPOT assay. Importantly, we show that contact-activated peritoneal B-1 cells migrate to these lymphoid tissues and then differentiate into Ag-specific IgM Ab-producing cells, resulting in specific CS-initiating IgM Abs in the serum by 1 day. Furthermore, pertussis toxin, which is known to inhibit signaling via G protein-coupled chemokines, inhibited the migration of contact-activated peritoneal B-1 cells to the lymphoid tissues, probably due to BLR-1 (Burkitt lymphoma receptor-1). These findings indicate that within 1 h after contact skin immunization, B-1 cells in the peritoneal cavity are activated to migrate to the lymphoid tissues by chemokine-dependent mechanisms to produce serum Ag-specific IgM Abs within 1 day after immunization, leading to local recruitment of CS-effector T cells.

Airway hyper-reactivity mediated by B-1 cell immunoglobulin M antibody generating complement C5a at 1 day post-immunization in a murine hapten model of non-atopic asthma.

Contact skin immunization of mice with reactive hapten antigen and subsequent airway challenge with the same hapten induces immediate airflow obstruction and subsequent airway hyper-reactivity (AHR) to methacholine challenge, which is dependent on B cells but not on T cells. This responsiveness to airway challenge with antigen is elicited as early as 1 day postimmunization and can be adoptively transferred to naïve recipients via 1-day immune cells. Responses are absent in 1-day immune B-cell-deficient JH(-/-) mice and B-1 B-cell-deficient xid male mice, as well as in recipients of 1-day immune cells depleted of cells with the B-1 cell phenotype (CD19(+) B220(+) CD5(+)). As B-1 cells produce immunoglobulin M (IgM), we sought and found significantly increased numbers of anti-hapten IgM-producing cells in the spleen and lymph nodes of 1-day immune wild-type mice, but not in xid mice. Then, we passively immunized naive mice with anti-hapten IgM monoclonal antibody and, following airway hapten challenge of the recipients, we showed both immediate airflow obstruction and AHR. In addition, AHR was absent in complement C5 and C5a receptor-deficient mice. In summary, this study of the very early elicited phase of a hapten asthma model suggests, for the first time, a role of B-1 cells in producing IgM to activate complement to rapidly mediate asthma airway reactivity only 1 day after immunization.

Early delayed-type hypersensitivity eosinophil infiltrates depend on T helper 2 cytokines and interferon-gamma via CXCR3 chemokines.

We investigated the role of T helper (Th)1- and Th2-type cytokines in delayed-type hypersensitivity to soluble protein antigens elicited early postimmunization. Mice were sensitized by intradermal injection without adjuvants, or subcutaneously with complete Freund's adjuvant, and subsequently ear challenged intradermally. As soon as day 3, antigen-specific eosinophil-rich responses were elicited in wild-type mice, but not in T-cell receptor-alpha-/- mice without adjuvant. Draining lymph node T cells stimulated with antigen secreted interleukin (IL)-4, IL-5 and interferon-gamma (IFN-gamma). IFN-gamma-dependent specific immunoglobulin G (IgG)2a and IL-4-dependent IgG1 were also generated. Delayed-type hypersensitivity ear swelling and local eosinophil recruitment were decreased in IL-5-/-, IL-4-/- and signal transducer and activator of transcription-6 (STAT-6)-/- mice, and with anti-IL-4 treatment of wild-type mice, suggesting Th2 mechanisms. Interestingly, responses were also decreased in IFN-gamma-/- mice, and IFN-gamma protein and the IFN-gamma-inducible CXC chemokine, IP-10, were present in 24-hr ear tissue extracts, suggesting Th1 effects. Finally, ear swelling, total histology and eosinophils were decreased in mice deficient in CXCR3, the chemokine receptor for IP-10. These results suggest that both a Th2-like (IL-5, IL-4 and STAT-6) and a Th1-like (IFN-gamma, IP-10, CXCR3) pathway contribute to eosinophil recruitment in early delayed-type hypersensitivity.

Cutaneous immunization rapidly activates liver invariant Valpha14 NKT cells stimulating B-1 B cells to initiate T cell recruitment for elicitation of contact sensitivity.

T cell recruitment to elicit contact sensitivity (CS) requires a CS-initiating process mediated by B-1 cells that produce IgM, which activates complement to promote T cell passage into the tissues. We now show that Valpha14i NKT cells induce B-1 cell activation likely by releasing IL-4 early postimmunization. The CS initiation process is absent in Jalpha18-/- and CD1d-/- NKT cell-deficient mice and is reconstituted by populations enriched for Valpha14i NKT cells. Transfers are not effective if cells are derived from IL-4-/- mice. Staining with specific tetramers directly showed that hepatic Valpha14i NKT cells increase by 30 min and nearly double by 2 h postimmunization. Transfer of immune B-1 cells also reconstitutes CS responses in NKT cell-deficient mice. The B-1 cells act downstream of the Valpha14i NKT cells to restore CS initiation. In addition, IL-4 given systemically to Jalpha18-/- or CD1d-/- NKT cell-deficient mice reconstitutes elicitation of CS. Further, splenocytes from immune Jalpha18-/- mice produce less antigen (Ag)-specific IgM antibodies compared with sensitized WT mice. Together these findings indicate that very early after skin immunization Valpha14i NKT cells are stimulated to produce IL-4, which activates B-1 cells to produce Ag-specific IgM, subsequently needed to recruit effector T cells for elicitation of CS responses.

B cell-dependent T cell responses: IgM antibodies are required to elicit contact sensitivity.

Contact sensitivity (CS) is a classic example of in vivo T cell immunity in which skin sensitization with reactive hapten leads to immunized T cells, which are then recruited locally to mediate antigen-specific inflammation after subsequent skin challenge. We have previously shown that T cell recruitment in CS is triggered by local activation of complement, which generates C5a that triggers C5a receptors most likely on mast cells. Here, we show that B-1 cell-derived antihapten IgM antibodies generated within 1 day (d) of immunization combine with local challenge antigen to activate complement to recruit the T cells. These findings overturn three widely accepted immune response paradigms by showing that (a) specific IgM antibodies are required to initiate CS, which is a classical model of T cell immunity thought exclusively due to T cells, (b) CS priming induces production of specific IgM antibodies within 1 d, although primary antibody responses typically begin by day 4, and (c) B-1 cells produce the 1-d IgM response to CS priming, although these cells generally are thought to be nonresponsive to antigenic stimulation. Coupled with previous evidence, our findings indicate that the elicitation of CS is initiated by rapidly formed IgM antibodies. The IgM and challenge antigen likely form local complexes that activate complement, generating C5a, leading to local vascular activation to recruit the antigen-primed effector T cells that mediate the CS response.

Nerve growth factor activates mast cells through the collaborative interaction with lysophosphatidylserine expressed on the membrane surface of activated platelets.

Effect of nerve growth factor (NGF) on platelet-associated mast cell activation was investigated. Although neither NGF alone nor platelets alone induced significant 5-hydroxytriptamine (5-HT) release from rat peritoneal mast cells, marked 5-HT release was detected when costimulated with NGF and calcium ionophore-activated platelets. This response reached maximal levels as early as 5 min after the initiation of the coincubation and was completely blocked by anti-NGF Ab or by an inhibitor for a tyrosine kinase of the trkA NGF receptor. Paraformaldehyde-fixed platelets activated with either calcium ionophore or thrombin exhibited the collaborative ability, suggesting the possible involvement of some membrane molecules expressed on activated platelets in mast cell activation. Because activation of platelets induced expression of phosphatidylserine (PS) and/or lysoPS on membrane surface, and since lysoPS, unlike PS, initiated the NGF-induced 5-HT release, lysoPS expressed on activated platelets may be involved in the mast cell activation. Moreover, intradermal injection of NGF and activated platelets into the rat skin increased local vascular permeability. These findings suggested that NGF collaboratively worked with membrane lysoPS of activated platelets to induce mast cell activation. Thus, NGF released in response to inflammatory stimuli may contribute to mast cell activation in collaboration with locally activated platelets in the process of inflammations and tissue repair.

Ceramide and sphingosine rapidly induce apoptosis of murine mast cells supported by interleukin-3 and stem cell factor.

OBJECTIVE: Ceramide and sphingosine, generated by sphingomyelinase-mediated hydrolysis of sphingomyelin, which packs tightly in the bilayer of the plasma membrane, have been proposed as intracellular mediators of apoptotic signals. However, precise function of endogenous sphingomyelin-cycle metabolites in mast cells has been unclear. Thus, we sought to define the involvement of ceramide and sphingosine in apoptotic pathways of mast cells. MATERIALS AND METHODS: We examined the effect of cell-permeable C(2)-ceramide, sphingosine, and sphingomyelinase on survival of murine bone marrow-derived cultured mast cells (BMCMC) supported by recombinant interleukin-3 (rIL-3) and/or recombinant stem cell factor (rSCF). Downstream signaling pathways of C(2)-ceramide and sphingosine were analyzed by using caspase inhibitors. RESULTS: C(2)-ceramide, sphingosine, and sphingomyelinase induced apoptosis in BMCMC in the presence of rIL-3 and/or rSCF, and Z-VAD-fmk (a broad caspase inhibitor), Z-DEVD-fmk (a caspase 3 inhibitor), and Z-IETD-fmk (a caspase 8 inhibitor) partially prevented apoptosis of BMCMC induced by C(2)-ceramide but not sphingosine. CONCLUSION: The present results suggest that ceramide and sphingosine may function as intracellular mediators of apoptotic signals in mast cells, which override survival signals from IL-3 and SCF. In addition, caspases may be partially involved in ceramide- but not sphingosine-mediated apoptosis of mast cells.