NZB cytotoxic lymphocyte responses. Kinetic analyses

Active role of T cells in promoting an in vitro autoantibody response to self erythrocytes in NZB mice

The in vitro anti-self erythrocyte antibody response of NZB spleen cells appears to be influenced directly by T cells. Thy-1+, L3T4+ helper T cells are required for: (i) the generation in vitro of MRBC-specific IgM and IgG AFC by spleen cells from 'autoimmune' (9-12-month old) NZB mice and (ii) the generation in vitro of MRBC-specific IgM and IgG AFC by spleen cells depleted of suppressor cells from pre-autoimmune (2-3-months-old) NZB mice which show no clinical signs of an anti-MRBC response. It is evident from the present and previous studies that the anti-MRBC autoantibody response is regulated in pre-autoimmune spleen cell populations by Ly2+ T cells. Ly2-T cells from both pre-autoimmune and autoimmune mice in sufficient numbers can overcome this normal regulation and promote the anti-MRBC response in cultures of unfractionated pre-autoimmune spleen cells. Ly2- T cells isolated from autoimmune NZB mice were consistently more active in this than the Ly2- T cells isolated from pre-autoimmune mice, suggesting an enrichment of MRBC-reactive Ly2- T cells in autoimmune NZB mice. The Ly2- T cells from autoimmune NZB mice greatly enhance the autoimmune anti-MRBC response relative to a modest enhancement of the response to a foreign antigen, SRBC, produced by the same cells. These data indicate that T cells play an important role both in supporting the autoantibody response to MRBC and in disrupting tolerance, leading to autoimmunity in NZB mice.

Differences in maternal lineages of New Zealand Black mice defined by restriction endonuclease analysis of mitochondrial DNA and by expression of maternally transmitted antigen

Two substrains of New Zealand Black (NZB) mice have been compared with respect to expression of a maternally transmitted cell surface antigen, Mta, defined by cloned cytolytic T cells, and for restriction enzyme polymorphisms of mitochondrial DNA (mtDNA). These independent assays of maternal cytoplasmic inheritance provide strong evidence for genetic contamination of the NZB/BlPt substrain (NZB/Bl mice from Michael Potter's separate colony at the National Institutes of Health), in which the typical NZB immunologic abnormalities are at least partially ameliorated. The decisive data are the restriction enzyme maps of mtDNA for NZB/BlPt, which were identical with those of the common "old inbred" strains and quite different from those of NZB/BlN (NZB/Bl mice from the breeding facility at the National Institutes of Health). It is probable that the contamination of the NZB/BlPt substrain is related to phenotypic changes in their autoimmune state. More interestingly, the data are consistent with, although they do not prove, involvement of the mitochondrial genome in expression of a cell surface molecule.

Studies of defective tolerance induction in NZB mice. Evidence for a marrow pre-T cell defect

NZB mice manifest a defect in tolerance induction by deaggregated heterologous gamma globulins. We have used an adoptive transfer system to study the defect. Thymectomized, intact, or thymectomized recipients given thymic epithelial grafts were studied after lethal irradiation and reconstitution with NZB, DBA/2, or (NZB x DBA(F1 marrow depleted of mature T cells. NZB thymocytes were responsible for the tolerance defect of NZB mice. The information for the defect was present in the NZB marrow prethymocyte. That defect could only be expressed when there was further maturation in association with a thymus. However, the normal DBA/2 thymic epithelium served as well as the abnormal NZB thymic epithelium. These studies resolve existing conflicts as to whether the NZB marrow or thymus is responsible for the loss of tolerance in association with autoimmunity.

T cell abnormalities in NZB mice occur independently of autoantibody production

By means of a series of crosses and backcrosses, ZB.CBA/N mice were prepared bearing largely NZB autosomal genes, but having X chromosomes derived only from CBA/N mice. The CBA/N X chromosome carries a gene, xid, that is associated with the lack of a B cell subset necessary for most of the spontaneous autoantibody production by NZB mice. These ZB.CBA/N mice failed to develop autoantibodies to T cells, erythrocytes, or DNA. The availability of mice that were mostly NZB, but which failed to make autoantibodies, especially anti-T cell antibodies, allowed us to study possible T cell regulatory defects in NZB mice in the absence of either antibodies reactive with such T cells or other autoantibodies. We found that such mice had derangements of T cell regulation as did the NZB mice. These observations strongly suggest that the t cell abnormalities of NZB mice are not caused by the B cell hyperactivity of these mice, but rather represent independent defects. Thus, NZB mice appear to have primary defects in both the B cell population and the T cell population. Whether or not these are separate, or derive from a common precursor cell abnormality, remains to be determined.