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Natural antibodies contribute to tissue homeostasis and protect against infections. They are secreted constitutively without external antigenic stimulation. The differentiation state and regulatory pathways that enable continuous natural antibody production by B-1 cells, the main cellular source in mice, remain incompletely understood. Here we demonstrate that natural IgM-secreting B-1 cells in the spleen and bone marrow are heterogeneous, consisting of (a) terminally differentiated B-1-derived plasma cells expressing the transcriptional regulator of differentiation, Blimp-1, (b) Blimp-1+, and (c) Blimp-1neg phenotypic B-1 cells. Blimp-1neg IgM-secreting B-1 cells are not simply intermediates of cellular differentiation. Instead, they secrete similar amounts of IgM in wild-type and Blimp-1-deficient (PRDM-1ΔEx1A) mice. Blimp-1neg B-1 cells are also a major source of IgG3. Consequently, deletion of Blimp-1 changes neither serum IgG3 levels nor the amount of IgG3 secreted per cell. Thus, the pool of natural antibody-secreting B-1 cells is heterogeneous and contains a distinct subset of cells that do not use Blimp-1 for initiation or maximal antibody secretion.

Introduction: Data from patient cohorts and mouse models of atopic dermatitis, food allergy and asthma strongly support a role for chitinase-3-like-1 protein (CHI3L1) in allergic disease. Methods: To address whether Chi3l1 also contributes to TH2 responses following nematode infection, we infected Chi3l1-/- mice with Heligmosomoides polygyrus (Hp) and analyzed T cell responses. Results: As anticipated, we observed impaired TH2 responses in Hp-infected Chi3l1-/- mice. However, we also found that T cell intrinsic expression of Chi3l1 was required for ICOS upregulation following activation of naïve CD4 T cells and was necessary for the development of the IL-4+ TFH subset, which supports germinal center B cell reactions and IgE responses. We also observed roles for Chi3l1 in TFH, germinal center B cell, and IgE responses to alum-adjuvanted vaccination. While Chi3l1 was critical for IgE humoral responses it was not required for vaccine or infection-induced IgG1 responses. Discussion: These results suggest that Chi3l1 modulates IgE responses, which are known to be highly dependent on IL-4-producing TFH cells. [ABSTRACT FROM AUTHOR]

Chronic rejection is the primary cause of long-term failure of transplanted organs and is often viewed as an antibody-dependent process. Chronic rejection, however, is also observed in mice and humans with no detectable circulating alloantibodies, suggesting that antibody-independent pathways may also contribute to pathogenesis of transplant rejection. Here, we have provided direct evidence that chronic rejection of vascularized heart allografts occurs in the complete absence of antibodies, but requires the presence of B cells. Mice that were deficient for antibodies but not B cells experienced the same chronic allograft vasculopathy (CAV), which is a pathognomonic feature of chronic rejection, as WT mice; however, mice that were deficient for both B cells and antibodies were protected from CAV. B cells contributed to CAV by supporting splenic lymphoid architecture, T cell cytokine production, and infiltration of T cells into graft vessels. In chimeric mice, in which B cells were present but could not present antigen, both T cell responses and CAV were markedly reduced. These findings establish that chronic rejection can occur in the complete absence of antibodies and that B cells contribute to this process by supporting T cell responses through antigen presentation and maintenance of lymphoid architecture., Introduction Chronic rejection causing late allograft failure remains a clinical challenge despite advances in immunosuppression (1). A characteristic feature of chronic rejection is concentric intimal hyperplasia, termed chronic allograft vasculopathy [...]

Alloimmune responses in kidney transplant (KT) patients previously hospitalized with COVID-19 are understudied. We analyzed a cohort of 112 kidney transplant recipients who were hospitalized following a positive SARS-CoV-2 test result during the first 20 months of the COVID-19 pandemic. We found a cumulative incidence of 17% for the development of new donor-specific antibodies (DSA) or increased levels of pre-existing DSA in hospitalized SARS-CoV-2-infected KT patients. This risk extended 8 months postinfection. These changes in DSA status were associated with late allograft dysfunction. Risk factors for new or increased DSA responses in this KT patient cohort included the presence of circulating DSA pre-COVID-19 diagnosis and time post-transplantation. COVID-19 vaccination prior to infection and remdesivir administration during infection were each associated with decreased likelihood of developing a new or increased DSA response. These data show that new or enhanced DSA responses frequently occur among KT patients requiring admission with COVID-19 and suggest that surveillance, vaccination, and antiviral therapies may be important tools to prevent alloimmunity in these individuals. [ABSTRACT FROM AUTHOR]

D38 is involved in normal airway function, IL-13-induced airway hyperresponsiveness (AHR), and is also regulated by tumor necrosis factor (TNF)-[alpha] in airway smooth muscle (ASM) cells. This study aimed to determine whether TNF-[alpha]-induced CD38 upregulation in ASM cells contributes to AHR, a hallmark of asthma. We hypothesized that AHR would be attenuated in TNF-[alpha]-exposed CD38-deficient (CD38KO) mice compared with wild-type (WT) controls. Mice (n = 6-8/group) were intranasally challenged with vehicle control or TNF-[alpha] (50 ng) once and every other day during 1 or 4 wk. Lung inflammation and AHR, measured by changes in lung resistance after inhaled methacholine, were assessed 24 h following the last challenge. Tracheal rings were incubated with TNF-[alpha] (50 ng/ml) to assess contractile changes in the ASM. While a single TNF-[alpha] challenge caused no airway inflammation, both multiple-challenge protocols induced equally significant inflammation in CD38KO and WT mice. A single intranasal TNF-[alpha] challenge induced AHR in the WT but not in the CD38KO mice, whereas both mice developed AHR after 1 wk of challenges. The AHR was suppressed by extending the challenges for 4 wk in both mice, although to a larger magnitude in the WT than in the CD38KO mice. TNF-[alpha] increased ASM contractile properties in tracheal rings from WT but not from CD38KO mice. In conclusion, CD38 contributes to TNF-[alpha]-induced AHR after a brief airway exposure to the cytokine, likely by mediating changes in ASM contractile responses, and is associated with greater AHR remission following chronic airway exposure to TNF-[alpha]. The mechanisms involved in this remission remain to be determined. tumor necrosis factor-[alpha]

Nicotinic acid adenine dinucleotide phosphate (NAADP) has recently been shown to act as a second messenger controlling intracellular [Ca.sub.2+] responses in mammalian cells. Many questions remain regarding this signaling pathway, including the role of the ryanodine receptor (RyR) in NAADP-induced [Ca.sub.2+] transients. Furthermore, the exact metabolic pathway responsible for the synthesis of NAADP in vivo has not been determined. Here, we demonstrate that the NAADP mediated [Ca.sub.2+] release system is present in human myometrial cells. We also demonstrate that human myometrial cells use the NAADP second messenger system to generate intracellular [Ca.sub.2+] transients in response to histamine. It has been proposed in the past that the NAADP system in mammalian cells is dependent on the presence of functional RyRs. Here, we observed that the histamine-induced [Ca.sub.2+] transients are dependent on both the NAADP and inositol 1,4,5-trisphosphate signaling pathways but are independent of RyRs. The enzyme CD38 has been shown to catalyze the synthesis of NAADP in vitro by the base-exchange reaction. Furthermore, it has been proposed that this enzyme is responsible for the intracellular generation of NAADP in vivo. Using CD38 knockout mice, we observed that both the basal and histamine stimulated levels of NAADP are independent of CD38 and the base-exchange reaction. Our group is the first to demonstrate that NAADP is a second messenger for histamine-elicited [Ca.sub.2+] transients in human myometrial cells. Furthermore, the NAADP mediated mechanism in mammalian cells can be independent of RyRs and CD38. Our data provides novel insights into the understanding of the mechanism of action and metabolism of this new second messenger system. cADP ribose; inositol 1,4,5-trisphosphate; endoplasmic reticulum; ryanodine channel; nicotinic acid adenine dinucleotide phosphate; CD38; base-exchange reaction

The transmembrane glycoprorein CD38 in airway smooth muscle is the source of cyclic-ADP ribose, an intracellular calcium-releasing molecule, and is subject to regulatory effects of cytokines such as interleukin (IL)- 13, a cytokine implicated in asthma. We investigated the role of CD38 in airway hyperresponsiveness using a mouse model of IL-13-induced airway disease. Wild-type (WT) and CD38-deficient (CD38KO) mice were intranasally challenged with 5 [micro]g of IL-13 three times on alternate days under isoflurane anesthesia. Lung resistance ([R.sub.L]) in response to inhaled methacholine was measured 24 h after the last challenge in pentobarbital-anesthetized, tracheostomized, and mechanically ventilated mice. Bronchoalveolar cytokines, bronchoalveolar and parenchymal inflammation, and smooth muscle contractility and relaxation using tracheal segments were also evaluated. Changes in methacholine-induced [R.sub.L] were significantly greater in the WT than in the CD38KO mice following intranasal IL-13 challenges. Airway reactivity after IL-13 exposure, as measured by the slope of the methacholine dose-response curve, was significantly higher in the WT than in the CD38KO mice. The rate of isometric force generation in tracheal segments (e.g., smooth muscle reactivity) was greater in the WT than in the CD38KO mice following incubation with IL-13. IL-13 treatment reduced isoproterenol-induced relaxations to similar magnitudes in tracheal segments obtained from WT and CD38KO mice. Both WT and CD38KO mice developed significant bronchoalveolar and parenchymal inflammation after IL-13 challenges compared with naive controls. The results indicate that CD38 contributes to airway hyperresponsiveness in lungs exposed to IL-13 at least partly by increasing airway smooth muscle reactivity to contractile agonists. interleukin-13; inflammation; asthma; eosinophil; airway smooth muscle

Oxytocin-induced [Ca.sup.2+] transients play an important role in myometrial contractions. Here, using a knockout model, we found that the enzyme CD38, responsible for the synthesis of the second messenger cyclic ADP-ribose (cADPR), plays an important role in the oxytocin-induced [Ca.sup.2+] transients and contraction. We also observed that CD38 is necessary for TNF-[alpha]-increased agonist-stimulated [Ca.sup.2+] transients in human myometrial cells. We provide experimental evidence that the TNF-[alpha] effect is mediated by increased expression of the enzyme CD38. First, we observed that TNF-[alpha] increased oxytocin-induced [Ca.sup.2+] transients and CD38 expression in human myometrial cells. Moreover, using small interference RNA technology, we observed that TNF-[alpha] stimulation of agonist-induced [Ca.sup.2+] transients was abolished by blocking the expression of CD38. In control experiments, we observed that activation of the component of the TNF-[alpha] signaling pathway, NF-[kappa]B, was not affected by the treatments. Finally, we observed that the effects of TNF-[alpha] on CD38 cyclase and oxytocin-induced [Ca.sup.2+] transients are abolished by progesterone. In conclusion, we provide the first experimental evidence that CD38 is important for myometrial [Ca.sup.2+] transients and contraction. Moreover, CD38 is necessary for the TNF-[alpha]-mediated augmentation of agonist-induced [Ca.sup.2+] transients in myometrial cells. We propose that the balance between cytokines and placental steroids regulates the expression of CD38 in vivo and cell responsiveness to oxytocin. cyclic adenosine diphosphate-ribose; small interference ribonucleic acid; endoplasmic reticulum; ryanodine channel; tumor necrosis factor-[alpha]

Bronchus-associated lymphoid tissue (BALT) is occasionally found in the lungs of mice and humans; however, its role in respiratory immunity is unknown. Here we show that mice lacking spleen, lymph nodes and Peyer's patches generate unexpectedly robust primary B- and T-cell responses to influenza, which seem to be initiated at sites of induced BALT (iBALT). Areas of iBALT have distinct B-cell follicles and T-cell areas, and support T and B-cell proliferation. The homeostatic chemokines CXCL13 and CCL21 are expressed independently of TNF[alpha] and lymphotoxin at sites of iBALT formation. In addition, mice with iBALT, but lacking peripheral lymphoid organs, clear influenza infection and survive higher doses of virus than do normal mice, indicating that immune responses generated in iBALT are not only protective, but potentially less pathologic, than systemic immune responses. Thus, iBALT functions as an inducible secondary lymphoid tissue for respiratory immune responses., Author(s): Juan E Moyron-Quiroz [1]; Javier Rangel-Moreno [1]; Kim Kusser [1]; Louise Hartson [1]; Frank Sprague [1]; Stephen Goodrich [1]; David L Woodland [1]; Frances E Lund [1]; Troy D [...]