The characteristic cell surface phenotype of thymocytes and peripheral CD4⁺ T cells in pIV^−/− mice is reproduced in bone marrow chimera experiments only if the irradiated recipient is a pIV^−/− mouse.

Filled profiles represent T cells derived from pIV^−/−progenitors grafted into a wild-type host. Open profiles represent T cells derived from wild-type progenitors grafted into a pIV^−/− host. T cells were identified as donor-derived by gating with the appropriate congenic marker (Ly5.1 or Ly5.2). Groups B, C, D, and E refer to the groups of bone marrow chimeras listed in Table1. The 6 histograms in the upper panel reveal that thymocytes derived from wild-type bone marrow progenitors present alterations identical to those described in pIV^−/− and I-Aα^−/−mice if they develop in a pIV^−/− host. The 4 histograms in the lower panel represent a similar analysis of splenic CD4⁺ T cells. Peripheral pIV^−/−CD4⁺ T cells display a normal surface phenotype when they develop in wild-type hosts, whereas wild-type CD4⁺ T cells that develop in pIV^−/− recipients up-regulate CD44 and express lower levels of TCR.