Sensitized (T6 x RFM)F1 donor B cells contribute to hypergammaglobulinemia and to poor primary responses in RFM mice with allogenic host versus graft disease.

Experimental host versus graft (HVG) disease is the fatal immunodeficiency syndrome which is induced in susceptible strains of inbred mice by the perinatal inoculation of related F1 hybrid spleen cells. The allogenic HVG reaction results in severe T-cell depletion, but hyperplasia of B cells, of which some are F1 donor in origin. To investigate the role of F1 donor B cells in the development of hyperglobulinemia in HVG mice which respond poorly to primary antigenic challenge, antibodies to horseradish peroxidase (HRP) of (T6 x RFM)F1 donor B-cell origin were used as markers for the engraftment of primed donor B cells in RFM hosts, and as sequential measures of the allogenic reaction on them. F1 donor B cells sensitized to HRP survived different stages of the HVG reaction after inoculation on Day 1 or Day 8 after birth. Tests for the anti-HRP antibody output of RFM host cells, and engrafted HRP-primed and unprimed (T6 x RFM)F1 donor cells suggested that the hyperglobulinemia seen in HVG mice was caused principally by antigen-primed, F1 donor B cells stimulated by the allogenic effect, with or without further exposure to the antigen(s) to which the donors had been sensitized prior to transplantation. The poor primary responses were attributed to the engraftment of the many donor B cells already committed, to the immunological immaturity of the host B cells, and to the lack of T-cell help for adult unprimed F1 donor B cells. Taken together with previous work, the data also suggest that antigen-primed donor B cells were engrafted in preference to equally histoincompatible donor T cells and unprimed donor B cells.