Signaling through ZAP-70 is required for CXCL12-mediated T-cell transendothelial migration

Transendothelial migration of activated lymphocytes from the blood into the tissues is an essential step for immune functions. The housekeeping chemokine CXCL12 (or stroma cell-derived factor-1alpha), a highly efficient chemoattractant for T lymphocytes, drives lymphocytes to sites where they are highly likely to encounter antigens. This suggests that cross-talk between the T-cell receptor (TCR) and CXCR4 (the CXCL12 receptor) might occur within these sites. Here we show that the zeta-associated protein 70 (ZAP-70), a key element in TCR signaling, is required for CXCR4 signal transduction. The pharmacologic inhibition of ZAP-70, or the absence of ZAP-70 in Jurkat T cells and in primary CD4(+) T cells obtained from a patient with ZAP deficiency, resulted in an impairment of transendothelial migration that was rescued by the transfection of ZAP-70. Moreover, the overexpression of mutated forms of ZAP-70, whose kinase domain was inactivated, also abrogated the migratory response of Jurkat T cells to CXCL12. In contrast, no involvement of ZAP-70 in T-cell arrest on inflammatory endothelium under flow conditions or in CXCL12-induced actin polymerization was observed. Furthermore, CXCL12 induced time-dependent phosphorylation of ZAP-70, Vav1, and extracellular signal-regulated kinases (ERKs); the latter were reduced in the absence of functional ZAP-70. However, though a dominant-negative Vav1 mutant (Vav1 L213A) blocked CXCL12-induced T-cell migration, pharmacologic inhibition of the ERK pathway did not affect migration, suggesting that ERK activation is dispensable for T-cell chemotaxis. We conclude that cross-talk between the ZAP-70 signaling pathway and the chemokine receptor CXCR4 is required for T-cell migration.     

HPA-1a phenotype-genotype discrepancy reveals a naturally occurring Arg93Gln substitution in the platelet beta 3 integrin that disrupts the HPA-1a epitope

A single nucleotide polymorphism (SNP) at position 196 in the beta 3 integrin causes a Leu33Pro substitution in the mature protein. Alloimmunization against the beta 3Leu33 form (human platelet antigen [HPA]-1a, Pl(A1), Zw(a)) in patients who are beta 3Pro33 homozygous (HPA-1b1b, Pl(A2A2), Zw(bb)) causes neonatal alloimmune thrombocytopenia, posttransfusion purpura, or refractoriness to platelet transfusion. Studies with recombinant proteins have demonstrated that amino acids 1 to 66 and 288 to 490 of the beta 3 integrin contribute to HPA-1a epitope formation. In determining the HPA-1a status of more than 6000 donors, we identified a donor with an HPA-1a(weak) phenotype and an HPA-1a1b genotype. The platelets from this donor had normal levels of surface alpha IIb beta 3 but reacted only weakly with monoclonal and polyclonal anti-HPA-1a by whole blood enzyme-linked immunosorbent assay (ELISA), flow cytometry, and sandwich ELISA. We reasoned that an alteration in the primary nucleotide sequence of the beta 3Leu33 allele of this donor was disrupting the HPA-1a epitope. In agreement with this hypothesis, sequencing platelet RNA-derived alpha IIb and beta 3 cDNA identified a novel G/A SNP at position 376 of the beta 3 integrin that encodes for an Arg93Gln replacement in the beta 3Leu33 allele. Coexpression of the beta 3Leu33Gln93 encoding cDNA in Chinese hamster ovary cells with human alpha IIb cDNA showed that the surface-expressed alpha IIb beta 3 reacted normally with beta 3 integrin-specific monoclonal antibodies but only weakly with monoclonal anti-HPA-1a. Our results show that an Arg93Gln mutation in the beta 3Leu33 encoding allele disrupts the HPA-1a epitope, suggesting that Arg93 contributes to the formation of the HPA-1a B-cell epitope.     

The impact of COVID-19 pandemic on rheumatology practice: a cross-sectional multinational study

Clinical Rheumatology - To evaluate the impact of the coronavirus disease 2019 (COVID-19) pandemic on rheumatology practice. A cross-sectional web survey was designed by the members of the Arab...     

The effectiveness of a twice‐daily skin‐moisturising regimen for reducing the incidence of skin tears

A cluster randomised controlled trial was conducted to evaluate the effectiveness of a twice‐daily moisturising regimen as compared to ‘usual’ skin care for reducing skin tear incidence. Aged care residents from 14 Western Australian facilities (980 beds) were invited to participate. The facilities were sorted into pairs and matched in terms of bed numbers and whether they provided high or low care. One facility from each matched pair was randomised to the intervention group. Consenting residents in an intervention facility received a twice‐daily application of a commercially available, standardised pH neutral, perfume‐free moisturiser on their extremities. Residents in the control facilities received ad hoc or no standardised skin‐moisturising regimen. Participant numbers were sufficient to detect a 5% difference in incidence rate between the two groups with 80% power and a significance level of P = 0·05, and the inter‐cluster correlation coefficient was 0·034. Data were collected over 6 months. A total of 1396 skin tears on 424 residents were recorded during the study. In the intervention group, the average monthly incidence rate was 5·76 per 1000 occupied bed days as compared to 10·57 in the control group. The application of moisturiser twice daily reduced the incidence of skin tears by almost 50% in residents living in aged care facilities.     

Mannose-binding lectin and ficolin-2 do not influence humoral immune response to hepatitis B vaccine

Background

Host genetics appear to be an important factor in the failure to generate a protective immune response after hepatitis B (HBV) vaccination. Mannose-binding lectin (MBL) and ficolin-2 (FCN2), two pattern recognition receptors of the lectin pathway of complement, influence the clinical outcome of HBV, and MBL deficiency has been shown to augment the humoral response to HBV vaccination in several experimental models. Here, we investigated the association of MBL and FCN2 with the humoral response to HBV vaccination in a candidate gene and functional study.

Patients and methods

A post hoc analysis of a prospective, interventional HBV vaccination study among human immunodeficiency virus type 1 (HIV-1) uninfected individuals in Kenya was conducted. Serum levels and polymorphisms of MBL and FCN2 were analysed in relation to the immune response to HBV vaccination.

Results

Protective hepatitis B surface antibody levels (≥10 mIU/mL) were evident in 251/293 (85.7%) individuals. Median MBL and FCN2 levels were similar in responders vs. non-responders with a weak trend towards lower median MBL levels in non-responders (1.0 vs. 1.6 μg/mL, p = 0.1). Similarly, there was no difference in four MBL and six FCN2 polymorphisms analysed in the two groups with the exception of an increased frequency of a homozygous MBL codon 57 mutation in non-responders (4 (9.5%) vs. 8 (3.2%), p = 0.05) corresponding to lower MBL levels. Results were similar after adjusting for age and sex.

Conclusions

Our study does not support a prominent role of the lectin pathway of complement in general and MBL and FCN2 in particular in the humoral immune response to HBV vaccination in African adults.     

Tissue-resident mucosal-associated invariant T (MAIT) cells in the human kidney represent a functionally distinct subset

Mucosal-associated invariant T (MAIT) cells are innate-like T-cells that recognize bacterial riboflavin metabolites. They are present in human blood but are abundant at barrier sites, including the liver, lungs, and kidneys, where they possess a CD69⁺/CD103^+/− tissue-resident phenotype. In renal tissue, MAIT cells likely defend against the ascending uropathogens responsible for urinary tract infections (UTIs), which are common, especially among renal transplant recipients (RTRs). Nevertheless, the functional role for MAIT cells in renal tissue and the influence of renal transplantation on MAIT cells remains unclear. Using multiparameter flow cytometry and the MR1-tetramer, we characterized MAIT cell phenotype and function in healthy renal tissue (n = 6), renal transplants explanted after allograft failure (n = 14) and in blood from healthy controls (n = 20) and RTRs before and 1-year after transplantation (n = 21). MAIT cells in renal tissue constitute a distinct CD69⁺CD103^+/− population that displays typical phenotypic features of tissue-resident T-cells and is skewed toward IL-2, GM-CSF, and IL-17A production upon stimulation. The circulating MAIT cell population was not decreased in number in RTRs pre- or post-transplantation. Tissue-resident MAIT cells in the kidney represent a functionally distinct population. This shows how MAIT cells in the kidney may be involved in the protection against microorganisms.