When the susceptibility of MYA-1 and CLL-CD134 to infection with HIV (FIV) pseudotypes bearing diverse FIV Envs are compared, CLL-CD134 display a similar pattern of susceptibility to infection to MYA-1 cells, but achieve significantly higher counts per minute compared with MYA-1 cells, indicating that CLL-CD134 offered an ideal replacement to MYA-1 cells as the substrate for subsequent FIV neutralizing antibody assays. The gene discussed is TNFRSF4; the disease is infection.