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Two sets of ((resistant x susceptible) F1----parent) and (parent----F1) chimeric mice were prepared. In the chimeric combinations involving BALB/c and DBA/1 mice, all (F1----F1) chimeras developed arthritis as well as potent anticollagen responses after immunization with collagen, whereas all (F1----BALB/c) and (BALB/c----F1) chimeras induced neither arthritis nor immune responses. This type of F1 T cells could be activated with APC from DBA/1 but not from BALB/c mice. Thus, the failure of the [F1 in equilibrium with BALB/c] chimeras to mount anticollagen responses was due to a defect at the APC level. Another arthritis-resistant strain, C57BL/6, exhibited adequate APC function, but reduced T cell responsiveness, representing an intermediate responder. In the chimeric combinations involving C57BL/6 and DBA/1 mice, (F1----F1) and (C57BL/6----C57BL/6) chimeras developed very high and very low incidence of arthritis, respectively. (C57BL/6----F1) chimeras developed an appreciable incidence of arthritis under conditions in which this group of chimeras generated intermediate levels of anticollagen responses. In contrast, (F1----C57BL/6) chimeras developed low incidence of disease despite induction of strong responses. Moreover, cells from collagen-immunized (F1----C57BL/6) chimeras, when transferred into T cell-depleted B cell mice of F1 or C57BL/6 strain, produced comparable immune responses in both groups but induced much more severe arthritis in F1 than in C57BL/6 recipients. These results indicate that: i) two types of arthritis-resistant strains can be identified, each of which has anticollagen APC defect as a low responder and reduced T cell responsiveness as an intermediate responder and ii) a discrepancy between the degree of anticollagen responses and clinical arthritis is attributed to the differential susceptibility to anticollagen immune responses.

Immunization of DBA/1 mice with type II collagen resulted in typical and progressive arthritis, which is associated with the production of high titer of anti-collagen antibody and the induction of cell-mediated immunity as exemplified by delayed type hypersensitivity response as well as lymphokine production. In contrast, administration of heat-denatured collagen into DBA/1 mice failed to induce the arthritis. These mice produced only marginal antibody, whereas they developed comparable cell-mediated immunity to that induced by immunization with native collagen, and therefore the inoculation of heat-denatured collagen provided the regimen capable of inducing preferentially cell-mediated immunity without the generation of high level of antibody. Inasmuch as administration of antibody induced only marginal and transient joint swelling not associated with typical histologic lesion, the synergistic effect of humoral and cell-mediated immunities was investigated using antibody preparation and the regimen to induce selectively cell-mediated immunity. The results demonstrate that administration of antibody into DBA/1 mice pre-sensitized with heat-denatured collagen resulted in potent and progressive arthritis. Such synergy was further confirmed by the induction of arthritis in T cell-depleted DBA/1 mice that had been adoptively transferred with antibody and lymphoid cells from heat-denatured collagen-sensitized mice. Moreover, it was revealed that the nature of cells capable of transferring cell-mediated immunity was of Thy-1+ and L3T4+ Lyt-2-. These results indicate that anti-collagen antibody and L3T4+ T cell-mediated cellular immunity are crucially required for the perpetuated development of type II collagen-induced arthritis.

The present study investigates the cellular and molecular mechanisms responsible for expressing genetic control of type II collagen-induced murine chronic arthritis. Analyses were made for both humoral and cellular immune responses, since the induction of arthritis required synergy between both types of immunities. Immunization of high (DBA/1) and low (C57BL/6, C3H/He, BALB/c) responder mice with native bovine type II collagen resulted in the production of the respective high and low levels of anti-collagen antibody. However, polyclonal in vitro stimulation of normal spleen cells from high or low responder mice with lipopolysaccharide (LPS) induced a comparable magnitude of anti-collagen antibody responses, indicating the localization of the genetic defect at cellular levels other than B cells themselves. In contrast to immunization with native collagen, sensitization of DBA/1 mice with heat-denatured collagen failed to stimulate B cells, but resulted in selective generation of L3T4+ T cell-mediated immunity. These included anti-collagen delayed-type-hypersensitivity (DTH) responses and the generation of various interleukins (IL) responsible for antibody production as well as DTH responses. It was demonstrated that there was appreciable difference in the magnitudes of these responses between lymphoid cells from high and low responder mice. Differential effects of sensitization with heat-denatured collagen in high versus low responders were reflected on the genetic difference in the development of chronic arthritis. A typical arthritis was induced neither in denatured collagen-sensitized DBA/1 mice nor in unsensitized mice transferred with anti-collagen antiserum. However, the antiserum transfer into denatured collagen-sensitized DBA/1 mice induced chronic perpetuating arthritis. This sharply contrasted with the failure of the same aliquot of the antiserum to induce a chronic arthritis when inoculated into denatured collagen-sensitized low responder mice. These results indicate that the genetic control of the induction of arthritis is expressed on L3T4+ T cells which are required for generating anti-collagen humoral as well as cell-mediated immunities as assessed by DTH responses in vivo or lymphokine productions in vitro.

We established an interleukin-6 (IL-6)-dependent cell line from murine plasmacytoma MOPC-104E cells. This cell line (designated PIL-6) was found to respond to murine and to human IL-6, but not to any other cytokines. We used this cell line to investigate the involvement of IL-6 production in type II collagen-induced arthritis in DBA/1 mice. Only marginal IL-6 activity was detected in sera from DBA/1 mice inoculated with Freund's complete adjuvant (FCA) alone, with an unrelated protein (bovine serum albumin) plus FCA, or with type II collagen plus Freund's incomplete adjuvant. However, enhanced IL-6 activity was observed in DBA/1 mice that had been injected with type II collagen plus FCA to induce arthritis. The elevated level of serum IL-6 activity was associated with high levels of IL-6 produced when lymph node cells from arthritic mice were stimulated in vitro with type II collagen. We also found that the L3T4+ T cell subset is responsible for the enhanced production of IL-6 in arthritic mice. The results are discussed in the context of potential roles of IL-6 in the induction and/or expression of chronic, progressive arthritis.