The effect of minocycline in rat models of inflammatory arthritis: correlation of arthritis suppression with enhanced T cell calcium flux.

Adjuvant and collagen arthritis in the rat are widely accepted T-cell-dependent counterparts of rheumatoid arthritis and were used to examine the antiinflammatory properties of minocycline. Administration of oral minocycline, a semisynthetic tetracycline, significantly decreased (P < 0.01) the incidence of arthritis in both models. In vivo exposure to minocycline also significantly increased the percentage of splenocytes exhibiting a rise in free intracellular calcium concentration ([Ca2+]i) following concanavalin A stimulation (P < 0.05 in adjuvant and P < 0.01 in collagen). This enhancement was mitogen dose-dependent and supported exclusively by extracellular Ca2+. Resting [Ca2+]i levels were unaffected by minocycline and predominantly the CD4+ subset was involved. No changes were observed in weight, IgG antibodies to collagen, synoviocyte release of collagenase and prostaglandin E2, acute inflammation in an air-pouch system, or cell surface expression of activation markers (interleukin-2 and transferrin receptors) by splenocytes or lymph node cells. As a controlled [Ca2+]i rise is a critical event in normal T cell activation, minocycline's antiarthritic profile in vivo may relate to perturbed Ca2+ influx during T cell activation, an alteration that could promote the development of clinical tolerance to otherwise arthritogenic stimuli.

Detection of arthritogenic factor in adjuvant arthritis.

An evocation of arthritis by an Ag-specific lymphokine has recently been considered with the description of arthritogenic factor (AF) in rats with collagen arthritis. Because rats with CFA-induced arthritis also exhibit T cell reactivity to native type II collagen, T cell lines specific for this protein were established from CFA-injected rats. Supernatant material from these lines contained a type II collagen-binding lymphokine with functional and biochemical attributes identical with those described for AF, i.e., it was a 65-kDa species cross-reacting immunoprotein possessing the ability to incite an erosive, proliferative synovitis when injected into the knee joint of naive recipients. Similarities were also observed with HPLC and on two-dimensional gels. Lymph node cells from rats with arthritis created by injection of the synthetic adjuvant, CP-20,961 failed to produce AF, suggesting that this material is not a ubiquitous concomitant of inflammatory arthritis in the rat. Test injections into sites contiguous with the ear cartilage plate and into fibroblast-lined s.c. pouches suggested that cartilage was a requisite for the induction of inflammation by AF. These data identify a potentially shared effector pathway in the collagen and adjuvant models. The presence of AF in two frequently used models further supports the hypothesis that Ag-specific lymphokines can create autoimmune disease.

Iron, iron-binding proteins and immune system cells.

In summary, the work reviewed in the present paper indicates that 1. Iron and the iron-binding proteins can act as regulators of immune function, and not only as a result of a nutritional dependence of lymphoid cells on transferrin and transferrin-iron. Subsets of cells of the immune system respond differently to increases in iron concentration in vitro and in vivo. 2. Macrophages and lymphocytes differ in the H and L subunit content of the ferritins synthesized in response to increases in iron concentration in vitro. 3. NK activity by adherent and nonadherent cells differ in their susceptibility to the enhancing effect of lactoferrin in vitro. 4. Responses to mitogen stimulation by PHA and Con A are diminished, while the PWM response remains unaffected by exposure to acidic ferritins or by increasing concentrations of iron in vitro and in vivo. 5. Pretreatment of effector but not target cells with iron results in diminished responses in the MLR, an effect that appears to be related to the HLA-A locus. 6. In situ hybridization studies indicate that transferrin is synthesized by a specific subset of the T lymphocytes. 7. Transient increases in serum iron concentration above the full saturation of transferrin, reproducing the clinical situation frequently seen in hereditary hemochromatosis, are followed by a series of cellular changes in the synovium that can be correlated to changes in the course of an experimental model of arthritis in the rat.