David D. Wood

Stimulation by human interleukin 1 of cartilage breakdown and production of collagenase and proteoglycanase by human chondrocytes but not by human osteoblasts in vitro

Human articular chondrocytes in culture synthesise collagenase and neutral proteoglycanase in response to addition of a 12-17 kDa protein produced by cultured human monocytes. This factor copurifies with interleukin 1, as assessed by lymphocyte activating factor activity, on gel filtration chromatography and isoelectric focusing. The interleukin 1 and chondrocyte-stimulating activities are destroyed by pretreatment of the material with phenylglyoxal. The same materials also promote the release of glycosaminoglycans from cultures of intact bovine nasal cartilage. The proteoglycanase activity release from chondrocytes appears to be a metalloproteinase because it is inhibited by EDTA and not by phenylmethylsulphonyl fluoride (PMSF), and because detection of its activity is dependent on the presence of 4-aminophenylmercuric acetate. Human osteoblast-like cells do not respond to this factor by increased proteinase production, but are stimulated to produce prostaglandins. These results suggest that interleukin 1 has activities upon non-immune cells which promote the degradation of connective tissue matrices. Human osteoblasts do not synthesise neutral collagen- and proteoglycan-degrading enzymes and thus are unlikely to be directly responsible for the matrix degradation which occurs during bone resorption.

Reduction of serum Interleukin-1-like activity after treatment with dexamethasone.

The ability of steroids to modulate the appearance of interleukin‐1(IL‐1) in vivo was evaluated in a model of endotoxin shock. High levels of IL‐1 were found in serum from A/J mice which were sensitized with P. acnes and challenged with bacterial lipopolysaccharide (LPS). The factor appeared in the serum 2–4 hours after LPS challenge and was dependent on the period of P. acnes sensitization and the dose of LPS. Treating the mice with dexamethasone prior to LPS challenge resulted in significantly lower thymocyte proliferative activity in the serum. Three experiments demonstrated that this reduced activity reflects a decrease in IL‐1. 1) The reduced activity was not due to the presence of proliferation inhibitors since mixing the serum from dexamethasone‐treated mice with purified IL‐1 or adding the equivalent amount of steroid directly to thymocyte cultures did not reduce the degree of proliferation. 2) When the serum was fractionated by gel filtration, the proliferative activity for both control and steroid treated sera eluted at 10–16 kilodaltons; however, the activity was nearly 50% less in the sample from steroid‐treated mice. 3) In addition to thymocyte proliferative activity, IL‐1 induces an increase in the serum titer of the acute phase protein known as serum amyloid A. Both serum‐ and gel‐ purified samples were able to induce the SAA, but again the samples from steroid‐treated mice were much less active. We conclude that the factor produced in vivo has the properties of IL‐1 and that the serum titre of the factor is reduced by dexamethasone treatment.

Interleukin 1 enhances synovial cell hyaluronate synthesis.

Abstract Interleukin 1 enhances proliferation of murine thymocytes in the presence of lectins, and is also known to stimulate the release of prostaglandins and neutral proteases from a variety of cell types. We have previously shown that a factor isolated from the culture media of disaggregated lining cells of the human synovial membrane was indistinguishable from monocyte-derived interleukin 1. We report here that interleukin 1 from either source stimulates hyaluronate synthesis by synovial membrane cells. Upon gel filtration or isoelectric focusing of synovial cell superna-tants, the hyaluronate-stimulatory activity co-fractionates with the interleukin 1 activity. Enhanced cell secretion of hyaluronate is a newly described metabolic effect of interleukin 1.

The effects of monocyte-conditioned medium and interleukin 1 on the synthesis of collagenous and non-collagenous proteins by mouse bone and human bone cells in vitro

Cultured adherent human mononuclear cells produce factor(s) which stimulate the release of calcium from new-born mouse calvaria in organ culture. This stimulation of bone resorption is accompanied by an inhibition of the incorporation of [3H]proline into collagen which is independent of increased prostaglandin production by the bone. When human osteoblast-like cells are treated with conditioned medium from human mononuclear cells, collagen accounts for a decreased proportion of the protein synthesised. This effect on matrix synthesis is not accompanied by an inhibitory action of the monocyte-conditioned medium preparations on net cell proliferation. In human osteoblast-like cell cultures, partially purified human interleukin 1 also inhibits the production of the bone-specific protein osteocalcin in a dose-dependent fashion. These observations are consistent with the hypothesis that products of human monocytes similar to, or identical with, human interleukin 1 may be important regulators of bone metabolism and may contribute to the bone loss seen in diseases such as chronic rheumatoid arthritis.

Resolution of a factor that enhances the antibody response of T cell-depleted murine splenocytes from several other monocyte products

Abstract A factor that enhances the antibody response of T cell-depleted murine splenocytes has been partially purified from culture fluids of human monocytes. The factor, referred to here as BAF, elutes from Sephadex in the region of 18,000-molecular-weight globular molecules. Comparison with other secreted monocyte products shows that BAF is distinct from plasminogen activator, colony-stimulation factor and the thymocyte mitogen.

Stimulation of the release of a B cell-activating factor from human monocytes.

Abstract Cultured human monocytes can release a factor that stimulates nude mouse splenocytes to produce immunoglobulin antibody against sheep erythocytes in vitro . The monocytes do not contain the factor in an active form when they are isolated; however, the factor is rapidly induced and released in the presence of Mycostatin, phytohemagglutinin, and bacterial endotoxin. These three stimulants all act directly on the monocyte causing similar kinetic patterns of release. Phagocytic stimuli do not appear to cause significant release of the factor.

Control of the mitogenicity of muramyl dipeptide

Abstract Muramyl dipeptide (MDP) has been shown to be the smallest subunit of bacterial peptidoglycan which exhibits adjuvanticity in vivo . Among its numerous in vitro activities is the ability to enhance the rate of DNA synthesis of murine splenocytes. In the present study, the dividing splenocytes were shown to be B cells which required prolonged incubation with MDP before becoming committed to division. T cells contributed minimally, if at all, to the DNA synthesis response observed nor did they function as helpers. Macrophage depleted lymphocytes responded poorly but could be reconstituted with fresh macrophages or 2-mercaptoethanol. X-ray irradiation of the macrophages reduced their ability to serve as accessory cells. Because of the biological similarity between bacterial endotoxin (LPS) and MDP, the possibility was tested that the gene(s) controlling the mitogenic response to MDP were either linked to or identical with the genes controlling the response to LPS. The results obtained from the comparison of selected mouse strains and from backcross analysis indicated that the two responses are not controlled by closely linked genes. These same strains of mice were compared with respect to their ability to respond to MDP as an adjuvant for the secondary antibody response to bovine albumin in vivo . It was found that the intensity of the in vivo adjuvant response was not correlated with the intensity of the in vitro mitogen response. We conclude from these observations that the ability of MDP to act as a mitogen makes little or no contribution to its adjuvanticity in vivo .

COMPARISON OF THE PLAQUE-STIMULATING AND THYMOCYTE-STIMULATING ACTIVITIES DERIVED FROM HUMAN MONOCYTES

Human monocytes have been reported to release factors that can elicit distinct responses from a number of different target cells. In this report, it is shown that most of the thymocyte-stimulating activity in supernatants of endotoxin-stimulated monocytes can be separated from the plaque-stimulating factor (BAF) by gel filtration and isoelectric focusing; however, since these activities could not be entirely resolved, the question was addressed whether the plaque-stimulating activity of BAF depends upon the stimulation of T-cells. Several critical experiments are reported which fail to support this hypothesis. On the other hand, these experiments led to the observation that the response to BAF depends on both an IgM-positive B-cell and a G10-adherent, plastic nonadherent, IgM-negative, irradiation-insensitive cell found in nude splenocytes. Finally, the possibility is discussed that this factor may be responsible for many of the physiological sequelae of infection.

ROLE OF ADHERENT CELL PRODUCTS IN THE IMMUNE RESPONSE

Publisher Summary This chapter reviews the role of adherent cell products in the immune response. One of the first experimental approaches that suggested that macrophages play a role in the immune response was the demonstration that injection of massive doses of carbon into an animal prior to antigenic challenge reduces its subsequent antibody response to antigens. The rate at which lymphocytes flow through lymphoid organs is controlled by the macrophage. The macrophages have been claimed to be the source of immunogenic RNA and have been shown to secrete immunoregulatory factors in vitro. BAF probably mediates a new pathway of immune response that is distinct from the classical pathway.

Response of CBA/N mice to human B cell activating factor

Abstract The in vitro antibody responses of CBA mutant and normal mice were studied with respect to their relative abilities to respond to stimulation by purified B cell activating factor (BAF). It was found that mice carrying the X-linked inability to respond to T-independent antigens can respond to BAF. This result is discussed with respect to the possibility that BAF exerts its effect on a subset of B cells distinct from those cells responsive to non-mitogenic T-independent antigens.