The phenomenon of albumin-hitchhiking has been exploited in vaccination strategies. We hypothesized that albumin mediated protein delivery may have evolved to facilitate the presentation of conformational determinants directly to B cells to facilitate B cell activation. However, the receptor that potentially targets albumin to lymph nodes and facilitates the presentation of intact proteins to B cells has hitherto not been identified.
Surface binding, specificity and saturability studies were performed on human and murine immune cells. Membrane proteins were extracted from human Ramos B cell membranes and affinity chromatography was performed using an HSA (human serum albumin)-Sepharose matrix. Mass spectrometry was performed on eluted proteins. CRISPR/Cas9 mediated gene ablation was used to establish the identity of the HSA-receptor (HSA-R). HEK 293T cells were transfected with the cDNA for the HSA-R. In vitro culture of murine dendritic cells with HSA and HSA-bound proteins and immunization of a range of genetically altered recipient mice was performed to establish the in vivo function of the HSA-R.
We purified the HSA-R using affinity chromatography and validated its identity using gene ablation and overexpression studies. CRISPR/Cas9 mediated gene ablation and overexpression in HEK 293T cells helped establish that the HSA-R is both necessary and sufficient to exhibit albumin on the surface of antigen presenting cells for at least 15 hours. In vivo experiments have established that this receptor on dendritic cells facilitates potent T dependent germinal center-based B cell responses.
A newly discovered poorly endocytic but specific albumin receptor on antigen presenting cells is likely crucial for facilitating antigen presentation to antigen-specific B cells and enhancing T-B cell collaboration against bacterial lipoproteins and other albumin-binding microbial proteins.
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Immune Response Regulation: Cellular Mechanisms (IRC)
S. Pillai, Willi Haas, Sumi Nechat et al.· Journal of Immunology· 0 citations
OBJECTIVE
Systemic sclerosis (SSc) is characterized by immune dysregulation and fibrosis. We investigated whether abatacept modulates CD319/SLAMF7-expressing cytotoxic T cells implicated in diffuse cutaneous SSc.
METHODS
In this ancillary ASSET trial analysis, PBMCs from 67 participants were analyzed at baseline and months 1, 3, and 6. Flow cytometry quantified CD4+CD319+ and CD8+CD319+ T cells, cytotoxic/activation markers, and stimulated intracellular IL-4, IL-17A, and IFN-γ. Analyses compared abatacept-treated molecular endotypes with placebo and related immune changes to modified Rodnan skin score (mRSS) change. Skin single-cell RNA sequencing included 5 healthy controls and 8 SSc patients.
RESULTS
At baseline, CD319+ T cells showed greater cytokine production, activation, and granzyme/perforin expression than CD319- T cells in 60 evaluable participants (p<0.001 to p<0.0001). Abatacept reduced CD4+CD319+ and CD8+CD319+ T cell frequencies at month 6; placebo did not. Effects were strongest in fibroproliferative patients, where CD8+CD319+ T cells decreased versus placebo (n=7 versus n=36; p=0.0377). In this endotype, abatacept reduced IL-4 in CD4+CD319+ and CD8+CD319+ T cells at month 3 (p=0.0468 and p=0.0287) and IL-17A in CD8+CD319+ T cells at month 6 (p=0.0004), while IFN-γ was unchanged. Reduction in CD4+CD319+ T cells correlated with mRSS improvement in abatacept-treated patients (r=0.5297, p=0.0423). Skin single-cell RNA-sequencing showed increased SLAMF7 expression in SSc T cells (p=0.017), enriched within cytotoxic subsets.
CONCLUSION
CD319+ T cells represent highly differentiated, activated cytotoxic effector populations in SSc. Abatacept selectively modulates these cells and suppresses associated pro-fibrotic and pro-inflammatory cytokines, particularly in the fibroproliferative subtype, where CD319+ T cell reductions correlate with clinical improvement.
Mikel Gurrea-Rubio, Laura A. Cooney, Kohei Maeda et al.· Arthritis & Rheumatology· 0 citations