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* Department of Medicine, Duke University Medical Center and Veterans Affairs Medical Center, Durham, NC 27710; and
Department of Medicine, St. Louis University and Veterans Affairs Medical Center, St. Louis, MO 63106
Basement membrane proteins are targeted in organ-limited and
systemic autoimmune nephritis, yet little is known about the origin or
regulation of immunity to these complex extracellular matrices. We used
mice transgenic for a nephrotropic systemic lupus erythematosus (SLE)
Ig H chain to test the hypothesis that humoral immunity to basement
membrane is actively regulated. The LamH-Cµ Ig H chain transgene
combines with diverse L chains to produce nephrotropic Ig reactive with
murine laminin
1. To determine the fate of transgene-bearing B cells
in vivo, transgenic mice were outcrossed onto nonautoimmune B6 and
SLE-prone MRL backgrounds and exposed to potent mitogen or Ag in
adjuvant. In this work we demonstrate that transgenic autoantibodies
are absent in serum from M6 and M29 lineage transgenic mice and
transgenic B cells hypoproliferate and fail to increase Ig production
upon exposure to endotoxin or when subjected to B cell receptor
cross-linking. Administration of LPS or immunization with autologous or
heterologous laminin, maneuvers that induce nonoverlapping endogenous
anti-laminin IgG responses, fails to induce a transgenic
anti-laminin response. The marked reduction in splenic B cell
number suggests that selected LamH-Cµ H chain and endogenous L chain
combinations generate autospecificities that lead to B cell deletion.
It thus appears that SLE-like anti-laminin B cells have access to
and engage a tolerizing self-Ag in vivo. Failure to induce autoimmunity
by global perturbations in immune regulation introduced by the MRL
autoimmune background and exposure to potent environmental challenge
suggests that humoral immunity to nephritogenic basement membrane
epitopes targeted in systemic autoimmunity is tightly
regulated.
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