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. 2024 Jul 30;15:1432226. doi: 10.3389/fimmu.2024.1432226

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Copyright © 2024 Hildenbrand, Cramer, Bertolotti, Kaiser, Kläsener, Nickel, Reth, Heim, Hengel, Burgert and Ruzsics

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Ramos B cell signaling is inhibited by HA-49K orthologs to comparable levels. Ramos B cell signaling was determined to assess the inhibitory potential of HA-49K orthologs in B cells. Previous incubation of Ramos cells with cell supernatants (red) containing various HA-49K orthologs was performed. Unstimulated cells (unstim.) were used as a negative control (grey), co-incubation with unreactive A549 supernatant (A549) served as a positive control indicated in blue. Cells were washed and stimulated via receptor cross-linking using α-λ Abs. The cellular calcium-response was detected by flow cytometry and the mean peak Ca2+-levels (columns) of 3 individual experiments (dots) including standard deviation are shown. Statistical differences compared to A549 were analyzed using two-way ANOVA test (A). Immunoblot analysis of pErk1/2 levels upon BCR stimulation of Ramos B cell lines with 1 µg/ml α-λ Abs for 2 min. Unstimulated cells (unstim.) served as negative control while α-λ treated cells (pos. crtl.) and co-incubation with A549 supernatant (A549) served as positive controls. Detection of β-actin levels was used as loading control. One representative blot for Ramos and CD45-/- Ramos cells is shown (B). The relative detection levels of pErk1/2 to β-actin ratios in Ramos cells were normalized to the positive ctrl. The mean (columns) of 3 individual experiments (dots) including standard deviation is shown. Statistical differences to the positive ctrl. were analyzed using the two-way ANOVA test. Only significant results were indicated in the panel (C). A two-fold dilution series of cell supernatants containing HA-49K-D64 (D) and purified HA-49K-D64 proteins starting at 8 µg per sample (E) was performed. Samples were either supplemented with 0.5 µg per sample hCD45-Fc (+hCD45-Fc, red) or without (hCD45-Fc, blue). After a 1 h incubation period, the binding of HA-49Ks to Ramos cells was detected using α-HA-based flow cytometry. Undiluted supernatant from untransfected A549 cells (A549) or the 8 µg MT protein were utilized as negative controls and shown as single values at the end of the x-axis separated by the grey dashed line. The mean MFI of 3 individual experiments is displayed for each, including standard deviation in the form of error bars. Erk1/2 phosphorylation was analyzed to investigate the prevention of the inhibitory effect HA 49K-D64 by hCD45-Fc receptors via immunoblotting. The supernatant containing HA-49K-D64 proteins was diluted 1:10 and 4 µg purified HA-49K-D64 proteins were incubated for 1 h with 500 ng hCD45-Fc decoy receptors as indicated in the figure. Subsequently, reagents were incubated with Ramos cells for 1 h Cells were lysed after BCR stimulation with 2 µg/ml α-λ Abs for 2 min. Sample loading was controlled by the detection of β-actin levels. One representative blot is presented (F).