Cytogenetic studies of RFM mice which are susceptible to host versus graft disease following the perinatal inoculations of (T6 x RFM)F1 spleen cells and of T6T6 mice which are not

Immunodeficiency in RFM/(T6xRFM)F1 mouse chimaeras with lethal host-versus-graft syndrome

Rather than central tolerance, the perinatal inoculation of related F1 hybrid spleen cells into inbred mice may result in host-versus-graft (HVG) reactions manifested as transient autoimmunity, or as a lethal immunodeficiency syndrome. RFM/(T6xRFM)F1 chimaeras with lethal disease die in 30 days with lymphosplenomegaly, immune complexes and impaired immune responses. The present studies used in vitro proliferation assays to show that the HVG reaction caused hyperplasia sufficient to account for the lymphosplenomegaly, while also causing severe impairment of splenic and nodal cell responses to concanavalin A (Con A) and to bacterial lipopolysaccharide (LPS). By 25 days, HVG mice could not distinguish between self and non-self as judged by mixed lymphocyte reactions (MLR) to RFM, (T6xRFM)F1 and third party A/J cells. There were no indications that host cells reactive to F1 donor cells had undergone clonal deletion, anergy or expansion. Flow cytometry revealed that donor T lymphocytes achieved stable engraftment, mostly in the nodes, despite the HVG reaction. Taken together with previous observations, these studies showed that HVG reactions in young parent F1/chimaeras can result in an immunodeficiency state which is characterized by an early appearing, profound and persistent impairment of both host and donor T and B cell functions. The results suggest that HVG reactions can contribute directly to immune deficits seen after clinical allogeneic bone marrow transplantation.

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.

Expression of murine leukemia viruses in RFM mice with host versus graft disease after perinatal inoculation of (T6 X RFM)F1 lymphohemopoietic cells

Host versus graft disease is the fatal syndrome of altered immunity that follows the perinatal inoculation of related F1 hybrid spleen cells to susceptible strains of inbred mice. The allogenic reaction results in severe depletion of T-lymphocytes, but causes hyperplasia and hypersecretion of B-cells. Among the long-term survivors of acute host versus graft reactions, there is a high incidence of nonthymic lymphomas associated with ecotropic murine leukemia virus that may be of donor F1 origin. The present studies were done to determine whether ecotropic murine leukemia virus played any role in the pathogenesis of acute host versus graft disease in RFM mice perinatally inoculated with (T6 X RFM)F1 spleen cells. In RFM/(T6 X RFM)F1 chimeras, N-tropic murine leukemia virus can be detected as early as 3 days. The progression of the disease was accompanied by increasing viral expression. The inoculation of N-tropic virus of F1 donor origin into RFM neonates failed to induce disease, although the virus proliferated. Detection of progressively rising titers of antibody to murine leukemia virus linked the virus to the development of hyperimmunoglobulinemia by virtue of its ability to serve as a replicating source of antigens. These and other studies provided evidence that the seemingly paradoxical appearance of hyperimmunoglobulinemia in T-cell-deficient mice with the host versus graft syndrome is due, at least in part, to the stimulation of presensitized F1 donor B-cells, which are not destroyed in the allogenic reaction, as are the T-cells. Another unusual finding was the detection of polytropic murine leukemia virus in 25-day-old RFM/(T6 X RFM)F1 chimeras. It is suggested that the allogenic host versus graft reaction favored the formation of recombinants.