SorLA contributes to B cell antigen presentation. (A) Representative fluorescent micrographs of anti-IgM surrogate antigen and MHC II in NTg and SORL1^KO Ramos-Cas9 cell lines. (B) Quantification of anti-IgM colocalization with MHC II molecules in NTg and SORL1^KO Ramos-Cas9 cell lines. Manders’ coefficient. n = 100–120 cells from three independent experiments. P value shown are calculated by two-way ANOVA. (C) Surface Eα-MHC II surface expression for WT and Sorl1^−/− cells relative to mean WT surface Eα-MHC II expression per experiment. n = 19–20 mice from four independent experiments. P value shown are calculated by unpaired t test. (D) HIV-1 Env SOSIP-derived peptides presented with HLA II by SORL1^KO and NTg control Ramos CH31 and Ramos DH270.1 HIV-1 bnAb IgM BCR-expressing B cell lines pulsed with CH505TFv4.1 SOSIP and CH848 10.17DT SOSIP, respectively. HIV-1 Env peptides identified in the HLA II–bound immunopeptidome of each cell line 24 h after the SOSIP antigen was added are indicated in heatmap format, aligned to the amino acid sequence of the CH505TFv4.1 SOSIP or CH848 10.17DT SOSIP. (E) Relative abundance of SOSIP-derived peptides (individual datapoints) presented by SORL1^KO versus NTg control cells. The peptide intensities in each sample were normalized to the total signal intensity of that sample using the IonQuant package. Relative abundance of peptides was calculated using the normalized signal intensities of each peptide and plotted as the log2 of the ratio of intensities of each peptide in the SORL1^KO versus NTg cells. P values shown are calculated by Wilcoxon ranked-signed test. Data in B and C show mean ± SEM.