Two new methods are described for making chromosomal spreads of single antibody-forming cells. The first depends on the controlled rupture of cells in small microdroplets through the use of a mild detergent and application of a mechanical stress on the cell. The second is a microadaptation of the conventional Ford technique. Both methods have a success rate of over 50%, though the quality of chromosomal spreads obtained is generally not as good as with conventional methods.

These techniques have been applied to an analysis of cell to cell interaction in adoptive immune responses, using the full syngeneic transfer system provided by the use of CBA and CBA/T6T6 donor-recipient combinations. When neonatally thymectomized mice were restored to adequate immune responsiveness to sheep erythrocytes by injections of either thymus cells or thoracic duct lymphocytes, it was shown that all the actual dividing antibody-forming cells were not of donor but of host origin. When lethally irradiated mice were injected with chromosomally marked but syngeneic mixtures of thymus and bone marrow cells, a rather feeble adoptive immune response ensued; all the antibody-forming cells identified were of bone marrow origin. When mixtures of bone marrow cells and thoracic duct lymphocytes were used, immune restoration was much more effective, and over three-quarters of the antibody-forming mitotic figures carried the bone marrow donor chromosomal marker.

The results were deemed to be consistent with the conclusions derived in the previous paper of this series, namely that thymus contains some, but a small number only of antigen-reactive cells (ARC), bone marrow contains antibody-forming cell precursors (AFCP) but no ARC, and thoracic duct lymph contains both ARC and AFCP with a probable predominance of the former. A vigorous immune response to sheep erythrocytes probably requires a collaboration between the two cell lineages, involving proliferation first of the ARC and then of the AFCP. The results stressed that the use of large numbers of pure thoracic duct lymphocytes in adoptive transfer work could lead to good adoptive immune responses, but that such results should not be construed as evidence against cell collaboration hypotheses.

Some possible further uses of single cell chromosome techniques were briefly discussed.

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