Guinea Pig IgG (Fab'2) [FITC]

Antibody and antibody-avidity assays relying on near-infrared-fluorescence amplification by nanostructured plasmonic gold substrates accurately quantify antibodies to SARS-CoV-2 and to common viruses in human serum and saliva. Accurate assays for the detection of antibodies to SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) are essential for the control of the COVID-19 (coronavirus disease 2019) pandemic. Here, we report antibody and antibody-avidity assays, relying on near-infrared-fluorescence amplification by nanostructured plasmonic gold substrates, for the simultaneous detection of antibodies to the S1 subunit of the spike protein and to the receptor binding domain of SARS-CoV-2 in human serum and saliva, and for quantifying immunoglobulin avidities against coronavirus antigens from SARS-CoV-2, SARS-CoV-1 and the common-cold viruses OC43, HKU1, NL63 and 229E. The antibody assay detected immunoglobulin M in 87% (52 of 60) COVID-19-positive serum samples collected 6 or more days after symptom onset (and the immunoglobulins M and G in all 33 samples collected at least 15 days after symptom onset), and correctly classified 456 out of the 457 COVID-19-negative serum samples tested (424 of them collected before the pandemic, including 73 that were positive for other viruses). We used the antibody-avidity assay to study antibody-maturation patterns, anamnestic responses, and cross-immunity to the common-cold coronaviruses.

Pemphigus vulgaris (PV) and bullous pemphigoid (BP) are autoantibody-mediated diseases clinically characterized by blisters and erosions of skin and/or mucous membranes. Immune imbalance and antibody generation are the key pathologies of autoimmune bullous diseases. Recently, a large number of studies have shown that T cell subsets, which are critical players in autoimmunity, exhibit a range of abnormalities and drive immunopathogenesis and skin inflammation in PV and BP. T helper (Th)1 cells mediate pro-inflammatory or immune responses through IFN-gamma and Th2-derived cytokines, such as IL-4, can promote B cell proliferation, antibody production and immunoglobulin class-switching. Th17 cells promote inflammatory response and skin damage, while regulatory T cells suppress autoreactive CD4(+) T cell activation and help control inflammation. T follicular helper cells cross-talk with B cells and facilitate autoantibody production. In this review, we discuss the immune features of PV and BP, with a focus on the aberrations in T cell subsets, such as Th1 cells, Th2 cells, Th17 cells, regulatory T cells, T follicular helper cells, CD8(+) T cells, gamma delta T cells and resident memory T cells in the pathogenesis of PV and BP. Improved understanding of biological and immunological functions of T cell subsets in patients with autoimmune skin disorders will offer unique opportunities for the recognition of treatment targets for these complex diseases.