Macromolecular insoluble cold globulin (MICG): a marker for embryonic prothymocytes in the mouse.

Adult thymocytes and peripheral T cells synthesize and insert a glycoprotein into their plasma membrane that is termed macromolecular insoluble cold globulin (MICG). This protein, in contrast to other T cell markers, was shown to be present in embryonic prothymocytes as soon as they appear in the thymic rudiment. Furthermore, some hematopoietic cells in the fetal liver were shown to contain MICG at a period in gestation before the completion of lymphocyte migration to the thymus. These results are discussed in terms of the requirements for embryonic cell migration.