Identification of a CD4 variant in Microminipigs not detectable with available anti-CD4 monoclonal antibodies

The Microminipig is an extra-small sized novel miniature pig developed in Japan. In the process of peripheral blood mononuclear cells analysis by flow cytometry, CD4+ cells could not be detected in some pigs with an anti-pig CD4 antibody (clone 74-12-4), or in some pigs with two other antibodies from different clones (MIL17 and PT90A). In a herd of 178 Microminipigs, 87 pigs (48.9%) were reactive with the anti-CD4 antibody (designated as CD4.A), and 91 pigs (51.1%) were non-reactive (designated as CD4.B). The CD4 types of piglets delivered from parents with CD4.A were CD4.A or CD4.B, and piglets delivered from parents with CD4.B were only CD4.B. This implies that the CD4.A pigs were homozygous for CD4.A or heterozygous for CD4.A and CD4.B, and the CD4.B pigs were homozygous for CD4.B. The CD4.B trait might be recessive. Significant differences could not be found in the percentage of CD3+ and CD8+ cells in whole lymphocytes between CD4.A and CD4.B animals. In the profile of CD4.B pigs, CD4+CD8+ T cells appeared to be detected in the CD4−CD8+ T cell region because the CD8 dull T cell population was observed. Thus, we considered that the CD4 molecules may be expressed on helper T cells, but the CD4 expressing cells could not be detected with the three anti-pig CD4 antibodies. Clinical abnormalities have not been observed in CD4.B pigs. Significant differences were not observed in immunoglobulin concentrations between CD4.A and CD4.B, though lower tendency was observed in plasma IgM concentrations from CD4.B pigs >36-months-old. These results imply that the CD4.B does not affect basic humoral immunity in vivo.