Migration of Long-lived Lymphocytes to the Bone Marrow and to Other Lymphomyeloid Tissues in Normal Parabiotic Guinea Pigs

Guinea pigs, in which cells with longlife span were selectively labeled (³H-thymidine), were joined in parabiosisto nonlabeled syngeneic litter mates ata time when label reutilization detectable by radioautography could be excluded. The distribution of labeledcells was investigated quantitativelyusing radioautography and liquid scintillation counting in the marrow andblood at the time of establishment ofparabiosis and again at its termination2 wk later, when the thoracic ductlymph, lymph nodes, spleen, and thymus were also examined. Single animals labeled in the same mannerserved as controls. Of all cells with aslow rate of turnover and long lifespan, only small lymphocytes enteredthe circulation and crossed the anastomosis in detectable numbers. As indicated by the similar percentages oflabeling in respective tissues, a complete intermixing of long-lived lymphocytes occurred in the bone marrow,lymph, lymph nodes, and spleen of theparabionts. The sum of the per centlabeled lymphocytes in two parabiontswas in agreement with the extent oflabeling in respective tissues of singlecontrols. The presence of a minor population of lymphocytes with a long lifespan was confirmed in the marrow.Ten to 30 times as many labeled long-lived lymphocytes migrated into thebone marrow of initially unlabeled animals as were found in an equal volumeof blood. The majority, if not all long-lived lymphocytes migrate to the marrow from the blood, and they also reenter the blood. They have a similarlife span and in parabionts equilibratein a similar manner as recirculatinglong-lived lymphocytes.

Submitted on October 22, 1971 Revised on January 3, 1972 Accepted on January 4, 1972