Figure 2. Evaluation of human antibody binding to class II SLA co-expressed with swine CD74.

Human sera were incubated with cells expressing pig CD74 and various class II SLA proteins or with parent cells lacking both class II SLA and CD74. 26 sensitized sera contained antibodies specific for class II HLA. 38 un-sensitized sera lacked anti-HLA antibodies. Fluorescent antibodies detected human immunoglobulin binding to cells (panel A, IgM binding-unsensitized sera; panel B, IgM binding-sensitized sera; panel C, IgG binding unsensitized sera; panel D, IgG binding-sensitized sera). Dot plots show the Log₁₀ of MFI ratios comparing immunoglobulin binding to SLA positive cells versus SLA-deficient parent cells. Values greater than 0 indicate more binding to class II positive cells. Log₁₀ values less than 0 represent greater immunoglobulin binding to the parent cell line. When antibodies bind equally to both cell types the Log₁₀ = 0. Heatmaps below the dot plots show binding results of sera having at least a single Log₁₀ ≥ 1. Each row represents an individual serum tested against every class II SLA heterodimer. Table 2 describes the class II allele-pair combinations. Gray squares represent class II (+) vs class II(−) MFI ratios ≤ 1. All other squares indicate increased binding to class II expressing cells. DR indicates SLA-DRα/DRβ pairs, DQ represents SLA-DQα/DQβ pairs, and H represent SLA-DRα/DQβ pairs.