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Based on our current information, the robust differences in responses of B6 and bm12 mice after immunization with AChR are as follows: (1) The AChR-specific T cell repertoires are strikingly different. The epitope specificities, as well as the rearranged TCR alpha and beta chains and their CDR3 domains, are virtually nonoverlapping in the two strains of mice. (2) The AChR antibody responses are quantitatively different, both to Torpedo AChR and to the autoantigen--mouse AChR. (3) The isotype distribution of AChR antibodies favors IgG2b in B6 mice, but not in bm12 mice. (4) The clinical manifestations of EAMG are qualitatively and quantitatively different in the two strains. These considerations have led to the following scheme, illustrated diagrammatically in FIGURE 2, to explain the differences in EAMG in B6 and bm12 mice: (1) The MHC Class II of B6 mice binds the alpha 146-162 peptide of Torpedo AChR with high affinity, while the genetically altered MHC Class II of bm12 mice does not, as previously suggested (see FIGURE 2). (2) The alpha 146-162/MHC Class II complex occurs only in B6 mice and interacts with T cells having appropriate TCRs, resulting in their stimulation and expansion. Although T cells of appropriate specificity are also available in the bm12 strain, the relevant peptide/MHC Class II complex is not present. Therefore, very few T cells with specificity for alpha 146-162 are stimulated, and those that are stimulated have different TCRs. T cells with specificity for other AChR peptides are also present and expanded in both strains of mice, but they have less influence on the outcome of the immune response. (3) The alpha 146-162-specific T cells of B6 mice, in turn, interact strongly with AChR-specific B cells of B6 mice. These B cells present the same epitope/MHC Class II complex as the APCs and therefore interact well with the alpha 146-162-specific T cells (FIGURE 2). Thus, T cells of this specificity appear to provide more efficient help for AChR antibody production than T cells with specificity for other Torpedo AChR epitopes. This results in production of greater amounts of AChR antibodies, including a critical subset that cross-reacts with autologous mouse AChR. The higher autoantibody levels contribute to the greater susceptibility to EAMG and to the greater severity of manifestations in the B6 strain compared with the bm12 strain. (4) There is a bias in B6 mice toward the production of AChR antibodies of IgG2b isotype. We suggest that T cells specific for alpha 146-162 may contribute to this isotype bias. The IgG2b antibodies appear to have particularly potent "myasthenogenic" effects in rats and mice. (5) Finally, it should be emphasized that these differences in immunological and clinical aspects of EAMG in B6 and bm12 mice are relative rather than absolute. T cells that respond to AChR epitopes other than alpha 146-162 can also provide help for AChR antibody production, albeit less potent. In a sense, this model represents a special case of molecular mimicry. In this case, the source of ...

An enzyme immunoassay was developed to detect human immunodeficiency virus type 1 (HIV-1) DNA amplified by polymerase chain reaction (PCR-EIA). A set of primers (outer set) was used in PCR to amplify a segment of the HIV-1 gag gene from peripheral blood mononuclear cells. Hybrids between the amplified DNA and a RNA probe were measured in a microtiter plate immunoassay using a beta-D-galactosidase-conjugated monoclonal antibody to DNA-RNA hybrids and a fluorescent substrate. A second set of primers (nested set) located within the outer set was used in PCR with a known template to prepare the probe. One primer of the nested set included the T7 RNA polymerase promoter at its 5' end allowing transcription of a single-stranded RNA probe. Ten copies of HIV-1 DNA could be detected by PCR-EIA (42 fluorescent units with a background of 18 fluorescent units) compared with a detection limit of 1000 copies by ethidium bromide-stained agarose gel. HIV-1 DNA was detected by PCR-EIA in peripheral blood mononuclear cells from 32 of 33 seropositive patients (range 54-810 fluorescent units), and 0 of 25 seronegative patients (range 20-40 fluorescent units) (sensitivity 97%; specificity 100%). PCR-EIA offers a practical and nonisotopic method to objectively measure PCR-amplified HIV-1 DNA and has the potential for the measurement of other microbial pathogens in human body fluids.

Myasthenia gravis (MG) is an autoimmune disease caused by T cell‐dependent antibody‐mediated reduction of acetylcholine receptors (AChR) at the neuromuscular junction. Immunization of animals with Torpedo californica AChR (TAChR) results in an experimental model of MG. We used the variable regions of α and β T cell receptor (TCR) genes recognizing an immunodominant peptide containing amino acids 146–162 from the α subunit of TAChR presented in the context of I‐Ab to generate TCR‐transgenic mice. We found that the transgenic TCR was strongly positively selected and that transgenic T cells proliferated robustly to the immunodominant peptide and TAChR. Unexpectedly, there was a variable paucity of B cells in the blood and spleen from transgenic mice, which averaged about 16% of peripheral blood lymphocytes, compared to 55% in wild‐type B6 mice. Unselected transgenic mice immunized with TAChR exhibited weak anti‐TAChR antibody responses. However, transgenic mice selected to have relatively higher B cell numbers produced anti‐TAChR titers equal to B6 mice and a predominance of Th1‐induced antibody isotypes were observed in certain experiments. The incidence and severity of clinical disease was variable following immunizations. These mice should be useful for studying the pathogenesis and treatment of MG.

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