Effect of mild α-chymotrypsin treatment of highly viscous semen samples on fertilization rates.

BACKGROUND: Highly viscous semen reduces sperm motility significantly and can contribute to infertility. When processing semen samples, few techniques exist to induce liquefaction in case of seminal hyperviscosity such as different washing steps and mechanical treatment. The use of α-chymotrypsin seems controversial due to possible negative effects on fertilisation rates after in vitro fertilization (IVF). The main objective of this study was to examine the influence of mild α-chymotrypsin treatment of semen samples on the fertilisation rate after artificial reproductive treatment (ART). METHODS: The fertilization rate of 52 ART cycles was examined following IVF using a low dose of α-chymotrypsin to induce liquefaction of highly viscous semen and was compared to a control group of 88 ART cycles. RESULTS: There was no significant difference in the fertilization rates of α-chymotrypsin treated semen samples compared to the control group; pregnancy rates were unaffected. CONCLUSIONS: The use of mild α-chymotrypsin treatment of semen samples in case of hyperviscosity does not appear to impact negatively on the fertilization rates after ART and could be regarded as an additional method to induce liquefaction of highly viscous semen samples in IVF.

Inefficient CAR-proximal signaling blunts antigen sensitivity.

Rational design of chimeric antigen receptors (CARs) with optimized anticancer performance mandates detailed knowledge of how CARs engage tumor antigens and how antigen engagement triggers activation. We analyzed CAR-mediated antigen recognition via quantitative, single-molecule, live-cell imaging and found the sensitivity of CAR T cells toward antigen approximately 1,000-times reduced as compared to T cell antigen-receptor-mediated recognition of nominal peptide-major histocompatibility complexes. While CARs outperformed T cell antigen receptors with regard to antigen binding within the immunological synapse, proximal signaling was significantly attenuated due to inefficient recruitment of the tyrosine-protein kinase ZAP-70 to ligated CARs and its reduced concomitant activation and subsequent release. Our study exposes signaling deficiencies of state-of-the-art CAR designs, which presently limit the efficacy of CAR T cell therapies to target tumors with diminished antigen expression.

Quantitative analysis of the sHLA-G protein in seminal plasma.

BACKGROUND: Recent studies revealed that maternal and embryonic contributions impact on HLA-G protein expression and might contribute to pregnancy success or failure. The main objective of this study was to examine the paternal levels of the immunoregulatory soluble human leukocyte antigen-G (sHLA-G) protein in seminal plasma and testicular biopsy samples during artificial reproductive technique (ART) treatment and to investigate possible correlations with other semen parameters, age, and pregnancy outcome of the female partner. METHODS: Soluble HLA-G levels of 106 seminal plasma samples and eight testicular biopsy samples were determined using a commercial sHLA-G Enzyme-linked immunosorbent assay (ELISA) kit. RESULTS: We observed a significant negative correlation of male age with total sHLA-G amount (P 0.023, R -0.221) and semen volume (P = 0.047, R -0.193). Testicular biopsy samples were analyzed and tested positively with sHLA-G ELISA. Levels of sHLA-G in seminal plasma samples from men with normozoospermia did not deviate significantly from those with reduced semen quality. No significant difference of sHLA-G levels in seminal plasma and pregnancy outcome of the female partner was detected. Our data showed that age of men with normozoospermia was significantly lower when the female partner conceived after ART treatment (P = 0.016, Mann-Whitney U test). CONCLUSION: High sHLA-G levels in seminal plasma of the male partner appear not to be required for pregnancy but might contribute among other factors to the success of establishing and maintaining pregnancy through long-term priming of the female uterine milieu.

Unperturbed Immune Function despite Mutation of C-Terminal Tyrosines in Syk Previously Implicated in Signaling and Activity Regulation.

The nonreceptor tyrosine kinase Syk, a central regulator of immune cell differentiation and activation, is a promising drug target for treatment of leukemia and allergic and inflammatory diseases. The clinical failure of Syk inhibitors underscores the importance of understanding the regulation of Syk function and activity. A series of previous studies emphasized the importance of three C-terminal tyrosines in Syk for kinase activity regulation, as docking sites for downstream effector molecules, and for Ca2+ mobilization. Here, we investigated the roles of these C-terminal tyrosines in the mouse. Surprisingly, expression of a triple tyrosine-to-phenylalanine human Syk mutant, SYK(Y3F), was not associated with discernible signaling defects either in reconstituted DT40 cells or in B or mast cells from mice expressing SYK(Y3F) instead of wild-type Syk. Remarkably, lymphocyte differentiation, calcium mobilization, and 2,4,6-trinitrophenyl (TNP)-specific immune responses were unperturbed in SYK(Y3F) mice. These results emphasize the capacity of immune cells to compensate for specific molecular defects, likely using redundant intermolecular interactions, and highlight the importance of in vivo analyses for understanding cellular signaling mechanisms.

The BAFFling function of Syk in B-cell homeostasis.

The TNF receptor family member BAFFR is essential for providing mature B cells with pro-survival signals and has recently been claimed to transduce these, though not exclusively, via a Syk-dependent signaling hub that feeds into ERK/AKT activation. In this issue of The EMBO Journal, Hobeika et al (2015) describe a synergistic prosurvival scenario involving BAFFR and CD19, which remains functional under Syk null conditions and is able to maintain mature B-cell survival. The authors hence propose a BAFFR-/CD19-driven mechanism to act in parallel with homeostatic NF-κB/AKT activation in non-stimulated B cells.

Suboptimal B-cell antigen receptor signaling activity in vivo elicits germinal center counterselection mechanisms.

Syk and Zap-70 constitute a closely related nonreceptor protein tyrosine kinase family, of which both members are functionally indispensable for conferring their respective antigen receptors with enzymatic activity. In this study, we analyze the impact of altering BCR signaling output on B-cell germinal center (GC) fate selection by constitutive, as well as inducible, monoallelic Syk kinase loss in the presence of a Zap-70 knock-in rescue allele. Cre-mediated Syk deletion in Syk(flox/Zap-70) B cells lowers pErk, but not pAkt-mediated signaling. Surprisingly, the use of a B-cell-specific constitutive mb1-cre deleter mouse model showed that a small cohort of peripheral Syk(flox/Zap-70);mb1-cre B cells efficiently circumvents deletion, which ultimately favors these Syk-sufficient cells to contribute to the GC reaction. Using a developmentally unbiased Syk(flox/Zap-70);mb1-creER(T2) approach in combination with an inducible tdRFP allele, we further demonstrate that this monoallelic deletion escape is not fully explained by leakiness of Cre expression, but is possibly the result of differential Syk locus accessibility in maturing B cells. Altogether, this underscores the importance of proper Syk kinase function not only during central and peripheral selection processes, but also during GC formation and maintenance.

Altered BCR signalling quality predisposes to autoimmune disease and a pre-diabetic state.

The spleen tyrosine kinase family members Syk and Zap-70 are pivotal signal transducers downstream of antigen receptors and exhibit overlapping expression patterns at early lymphocytic developmental stages. To assess their differential kinase fitness in vivo, we generated mice, which carry a Zap-70 cDNA knock-in controlled by intrinsic Syk promoter elements that disrupts wild-type Syk expression. Kinase replacement severely compromised Erk1/2-mediated survival and proper selection of developing B cells at central and peripheral checkpoints, demonstrating critical dependence on BCR signalling quality. Furthermore, ITAM- and hemITAM-mediated activation of platelets and neutrophils was completely blunted, while surprisingly FcγR-mediated phagocytosis in macrophages was retained. The alteration in BCR signalling quality resulted in preferential development and survival of marginal zone B cells and prominent autoreactivity, causing the generation of anti-insulin antibodies and age-related glomerulonephritis. Development of concomitant fasting glucose intolerance in knock-in mice highlights aberrant B cell selection as a potential risk factor for type 1 diabetes, and suggests altered BCR signalling as a mechanism to cause biased cellular and Ig repertoire selection, ultimately contributing to B cell-mediated autoimmune predisposition.

HPK1 competes with ADAP for SLP-76 binding and via Rap1 negatively affects T-cell adhesion.

The hematopoietic progenitor kinase 1 (HPK1) signals into MAPK and NFκB pathways downstream of immunoreceptors, but enigmatically is a negative regulator of leukocytes. Here, we report a novel role for HPK1 in regulating the activation of the adhesion molecule leukocyte function-associated antigen-1 (LFA-1). Upon TCR stimulation, mediated by binding of adhesion and degranulation promoting adaptor protein (ADAP) to SLP-76, a ternary complex composed of ADAP/55-kDa src kinase associated phosphoprotein (SKAP-55) and RIAM translocates to the membrane and causes membrane recruitment of the active small GTPase Ras-related protein 1 (Rap1). Active Rap1, via its binding to RapL (regulator for cell adhesion and polarization enriched in lymphoid tissues), mediates LFA-1 integrin activation. We show here that HPK1, which also binds SLP-76, compete with ADAP for SLP-76 binding. In addition, HPK1 dampens Rap1 activation, resulting in decreased LFA-1 activity. Analysis of HPK1-deficient T cells revealed increased ADAP recruitment to SLP-76 and elevated Rap1 activation in those cells, leading to increased adhesion to ICAM-1 and cell spreading. Altogether, these results describe a novel function for HPK1 in linking TCR signaling to cell adhesion regulation and provide a mechanistic explanation for the negative regulatory role of HPK1 in T-cell biology.

HAX1 deficiency: impact on lymphopoiesis and B-cell development.

HAX1 was originally described as HS1-associated protein with a suggested function in receptor-mediated apoptotic and proliferative responses of lymphoid cells. Recent publications refer to a complex and multifunctional role of this protein. To investigate the in vivo function of HAX1 (HS1-associated protein X1) in B cells, we generated a Hax1-deficient mouse strain. Targeted deletion of Hax1 resulted in premature death around the age of 12 wk accompanied by a severe reduction of lymphocytes in spleen, thymus and bone marrow. In the bone marrow, all B-cell populations were lost comparably. In the spleen, B220(+) cells were reduced by almost 70%. However, as investigated by adoptive transfer experiments, this impairment is not exclusively B-cell intrinsic and we hypothesize that a HAX1-deficient environment cannot sufficiently provide the essential factors for proper lymphocyte development, trafficking and survival. Hax1(-/-) B cells show a significantly reduced expression of CXCR4, which might have an influence on the observed defects in B-cell development.

HPK1 associates with SKAP-HOM to negatively regulate Rap1-mediated B-lymphocyte adhesion.

BACKGROUND: Hematopoietic progenitor kinase 1 (HPK1) is a Ste20-related serine/threonine kinase activated by a range of environmental stimuli including genotoxic stress, growth factors, inflammatory cytokines and antigen receptor triggering. Being inducibly recruited to membrane-proximal signalling scaffolds to regulate NFAT, AP-1 and NFkappaB-mediated gene transcription in T-cells, the function of HPK1 in B-cells to date remains rather ill-defined. METHODOLOGY/PRINCIPAL FINDINGS: By using two loss of function models, we show that HPK1 displays a novel function in regulating B-cell integrin activity. Wehi 231 lymphoma cells lacking HPK1 after shRNA mediated knockdown exhibit increased basic activation levels of Ras-related protein 1 (Rap1), accompanied by a severe lymphocyte function-associated antigen-1 (LFA-1) dependent homotypic aggregation and increased adhesion to intercellular adhesion molecule 1 (ICAM-1). The observed phenotype of enhanced integrin activity is caused downstream of Src, by a signalling module independent of PI3K and PLC, involving HPK1, SKAP55 homologue (SKAP-HOM) and Rap1-GTP-interacting adaptor molecule (RIAM). This alters actin dynamics and renders focal adhesion kinase (FAK) constitutively phosphorylated. Bone marrow and splenic B-cell development of HPK1(-/-) mice are largely unaffected, except age-related tendencies for increased splenic cellularity and BCR downregulation. In addition, naïve splenic knockout B-cells appear hyperresponsive to a range of stimuli applied ex vivo as recently demonstrated by others for T-cells. CONCLUSIONS/SIGNIFICANCE: We therefore conclude that HPK1 exhibits a dual function in B-cells by negatively regulating integrin activity and controlling cellular activation, which makes it an interesting candidate to study in pathological settings like autoimmunity and cancer.

Migration of antibody secreting cells towards CXCL12 depends on the isotype that forms the BCR.

Truncation of the cytoplasmic tail of membrane-bound IgE in vivo results in lower serum IgE levels, decreased numbers of IgE-secreting plasma cells and the abrogation of specific secondary immune responses. Here we present mouse strain KN1 that expresses a chimeric epsilon-gamma1 BCR, consisting of the extracellular domains of the epsilon gene and the transmembrane and cytoplasmic domains of the gamma1 gene. Thus, differences in the IgE immune response of KN1 mice reflect the influence of the "gamma1-mediated signalling" of mIgE bearing B cells. KN1 mice show an increased serum IgE level, resulting from an elevated number of IgE-secreting cells. Although the primary IgE immune response in KN1 mice is inconspicuous, the secondary response is far more robust. Most strikingly, IgE-antibody secreting cells with "gamma1-signalling history" migrate more efficiently towards the chemokine CXCL12, which guides plasmablasts to plasma cell niches, than IgE-antibody secreting cells with WT "epsilon-signalling history". We conclude that IgE plasmablasts have an intrinsic, lower chance to contribute to the long-lived plasma cell pool than IgG1 plasmablasts.

Membrane IgM influences membrane IgD mediated antigen internalization in the B cell line Bcl1.

Signalling through the B cell antigen receptor (BCR) is required for peripheral B lymphocyte maturation, maintenance, activation and silencing. In mature B cells, the antigen receptor normally consists of two isotypes: membrane IgM and IgD (mIgM, mIgD). Although the signals initiated from both isotypes differ in kinetics and intensity, in vivo, the BCR of either isotype seems to be able to compensate for the loss of the other, reflected by the mild phenotypes of mice deficient for mIgM or mIgD. Thus, it is still unclear why mature B cells need expression of mIgD in addition to mIgM. In the present paper, we used the B cell line Bcl1 and investigated the isotype-specific antigen internalization in dependence of co-stimulation of the reciprocal isotype and analysed whether the signal initiated from mIgM is modulated through signalling from mIgD and vice versa. We clearly showed that cross-linkage of mIgM decreases the rate of mIgD mediated antigen internalization and interpret this influence as a unilateral mIgM mediated control on signals initiated at mIgD.