Modulation of macrophage Ia expression by lipopolysaccharide: stem cell requirements, accessory lymphocyte involvement, and IA-inducing factor production

Mycoplasma fermentans-derived lipid inhibits class II major histocompatibility complex expression without mediation by interleukin-6, interleukin-10, tumor necrosis factor, transforming growth factor-beta, type I interferon, prostaglandins or nitric oxide

Mycoplasma cause several diseases in man and animals. Some strains can chronically infect humans, leading to fever or inflammatory syndromes such as arthritis, particularly in immunosuppressed patients. A set of pathogenicity factors shared by many mollicutes may be membrane components that activate macrophages to secrete cytokines and other inflammatory mediators. Mycoplasma-derived high molecular weight material (MDHM) is a macrophage-activating amphiphilic lipid which was purified from Mycoplasma fermentans. We studied the influence of MDHM on the expression of major histocompatibility complex (MHC) class II molecules by mouse resident peritoneal macrophages with an ELISA. Highly purified MDHM at 4 ng/ml and 0.8 microgram/ml crude heat-killed M. fermentans (concentrations chosen to give maximal responses) suppressed interferon (IFN)-gamma-dependent class II MHC induction when added simultaneously with IFN-gamma. MDHM was not toxic and did not result in loss of adherent cells. Kinetic data showed that MDHM first up-regulated, then down-regulated the expression of preformed class II MHC molecules, while expression of Mac-1 and F4/80 antigens remained constant. MDHM-dependent suppression of class II MHC molecule expression resulted in impaired antigen presentation to the helper T cell line D10.G4.1. We further attempted to identify hypothetical products of MDHM-stimulated macrophages as secondary mediators of class II MHC suppression such as were described for lipopolysaccharide (LPS)-stimulated macrophages. Type I IFN, prostaglandins and nitric oxide, all reported to cause down-regulation of class II MHC, could be excluded in this context. Of the cytokines tumor necrosis factor, interleukin (IL)-6, IL-10 and transforming growth factor-beta, only IL-10 inhibited class II MHC expression, although less effectively than MDHM. The involvement of IL-10 was ruled out, as no evidence for its MDHM-dependent formation could be found. Our data suggest that MDHM interferes with class II MHC expression by up-regulating its turnover, and at the same time, inhibits the formation of new class II MHC molecules.

In vivo induction of macrophage Ia antigen (MHC class II) expression by biomedical polymers in the cage implant system

Examination of the cellular components in the inflammatory exudate, which infiltrates subcutaneous cages, can be used to monitor the progress of an inflammatory response to an implanted material. Of particular interest is the study of monocyte/macrophage infiltration into the implanted cages containing biomaterials, as macrophages may initiate a wide spectrum of responses upon interaction with a foreign material. In this study, the authors propose a technique using subcutaneous tissue cages in conjunction with cytofluorimetric analysis of exudate leukocytes to evaluate the monocyte/macrophage cell activation in response to different materials. The studies reported here used several materials (thermoplastic and elastomeric polymers) as the challenging agent, to demonstrate whether polymers, chemically different from each other, could differentially activate macrophages to carry out their proinflammatory role more effectively. The materials tested included: poly(etherurethane ureas) (PEUU A'), poly(etherurethane ureas) with a surface active additive, Methacrol, (PEUU C'), polymethylsiloxane (PDMS), polyetherimide, (PEI), and polyetheretherketone, (PEEK). For all tested materials, the maximum numbers of exudate cells and of Ia-positive macrophages were found on day 7, although the entity of the cell increase was associated with the material used for the implant. Similarly, the percentage of Ia-positive macrophages varied according to the specific polymer present in the cages after 7 days. By day 14, the percentage of Ia-positive macrophages decreased with individual exudates showing 19-32% Ia-positive cells depending on the different type of material. Only in the case of PDMS did the percentage of Ia-positive macrophages remain the same as compared with control empty cage macrophages.

Antigen-specific proliferative response of peritoneal exudate lymphocytes primed with antigen and bacterial lipopolysaccharide: the roles of Ia+ accessory cells and IL-2

In vitro antigen-specific proliferation was investigated in a lymphocyte population that had been taken from the peritoneal exudate cells (PEC) of C3H/HeN mice (Iak) primed in vivo with both bacterial lipopolysaccharide (LPS) and horse red blood cells (HRBC) and had been purified by passage through a nylon fiber column (Nfc). The proliferative response of the Nfc-passed lymphocytes primed with HRBC and LPS [T(HRBC+LPS) cells] depended on the dose of antigen in the cultures, and the response was higher than that of cells prepared from mice primed with HRBC alone [T(HRBC) cells]. No response was seen in the cells prepared from the LPS-primed mice [T(LPS) cells] or normal mice [T(N) cells]. The response of the T(HRBC) cells was abolished by previous treatment of the cells with anti-Iak antibody and complement (C), whereas the response of the T(HRBC+LPS) cells was retained after the same treatment, indicating that the Ia- T(HRBC+LPS) cells can proliferate in response to antigen in spite of Ia+ accessory cell-depletion. Supernatants from the cultures of Ia- T(HRBC+LPS) cells in the presence of HRBC showed abundant IL-2 activity, while those of Ia- T(HRBC) cells did not. The IL-2 should be produced by the L3T4 cell population in T(HRBC+LPS) cells in response to antigen, since the previous treatment of the cells with anti-L3T4 antibody and C abrogated the production.(ABSTRACT TRUNCATED AT 250 WORDS)

Inducible accessory function of a macrophage cell line

Costimulatory molecules in addition to occupancy of the T-cell antigen receptor, are required to induce T-cell proliferation. Previous work suggested that membrane molecules responsible for costimulatory activity were not constitutively expressed on the antigen presenting cell (APC) surface. In the present study, we have identified a cloned macrophage cell line (FLJ2) with inducible APC function. The unactivated FLJ2 line could not induce T-cell proliferation. FLJ2 could present alloantigen, and stimulate proliferation of either a T-cell clone or normal resting T cells following activation with IFN gamma or unexpectedly with lipopolysaccharide (LPS)-Activated FLJ2 cells could be fixed and APC function was preserved. The relevant inducible molecules required for APC function appeared distinct from Ia and IL1. The expression of ICAM-1 and LFA-1 was increased during activation and anti-LFA-1 antibody blocked APC function. This suggests that one important feature of the activation process may be improvement of cellular adhesion.

Lipopolysaccharide, lipid A, and liposomes containing lipid A as immunologic adjuvants

Numerous studies have demonstrated that most or all of the potent adjuvant activity of Gram-negative bacterial endotoxin resides in the lipid A moiety of lipopolysaccharide (LPS). Synthetic analogues of lipid A have provided insights into structure-activity relationships. Several cellular mechanisms of LPS and lipid A adjuvant activities have been identified. Activation of macrophages by LPS or lipid A results in cytokine secretions that enhance the immune response. LPS and lipid A cause recruitment of antigen-presenting cells, particularly macrophages. Liposomes containing lipid A serve as an in vivo adjuvant to recruit increased numbers of macrophages. Liposomal lipid A that has been phagocytized by cultured macrophages also serves as an "intracellular adjuvant" to cause increased immunologic presentation of liposomal antigen by the macrophages to specific T lymphocytes. Lipid A can abolish suppressor T cell activity, resulting in increased immune responses to polysaccharide antigens. Upon combination of lipid A or lipid A analogues with nonionic block polymers, modulation of murine antibody isotypes can be achieved with antibodies against a variety of antigens in vivo. Liposomes containing monophosphoryl lipid A (MPL) have been utilized in a phase I clinical trial of a proposed malaria vaccine in humans. The liposomal malaria vaccine resulted in very high levels of antibodies against the malarial antigen, and despite the presence of huge amounts of MPL (up to 2.2 mg), the liposomal lipid A was nonpyrogenic and safe for use in humans. Lipid A and lipid A analogues, and liposomes or other carriers containing lipid A, have shown considerable promise both as adjuvants for immunization of animals and for human vaccines.