Macrophages as accessory cells in the in vivo humoral immune response: from processing of particulate antigens to regulation by suppression.

The ability of macrophages to act as accessory cells for the antigen mediated stimulation of T lymphocytes has been unequivocally established in in vitro experiments. However, in vivo experiments are required to investigate whether the in vitro abilities of cells reflect their in vivo function. In order to study whether or not macrophages are required for the induction of antibody production in vivo, a liposome mediated macrophage elimination technique has been developed.

Monoclonal antibody mediated targeting of enzymes. A comparative study using the mouse spleen as a model system.

The aim of this study was to target enzymes specifically to cells in the murine spleen. Monomeric and polymeric conjugates of the enzymes horseradish peroxidase or alkaline phosphatase and monoclonal antibodies against cell surface determinants were prepared. Highly specific in vivo targeting of enzymes to macrophages was obtained only when monomeric MAb-enzyme conjugates were used.

Liposome mediated affection of monocytes.

Dichloromethylene diphosphonate (Cl2MDP) enclosed in liposomes, when injected intravenously, selectively eliminates all phagocytizing macrophages that are in direct contact with the blood circulation of the spleen and the liver. We examined whether Cl2MDP containing liposomes affect, in addition, rat monocytes and bone marrow macrophage precursors (BMMP's). In addition to Phosphatidylcholine-Cholesterol liposomes (PC liposomes), we also used mannosylated PC liposomes (PCMAN liposomes), which are reported to bind more efficiently to macrophages.

Production of monomeric antigen-enzyme conjugate to study requirements for follicular immune complex trapping.

Studies concerning the localization of immune complexes in lymphoid follicles and the involvement of these trapped immune complexes in the regulation of the immune response have thus far been performed with poorly defined complexes in terms of size and composition. For that reason, the minimum requirements for trapping in terms of number of antigen- and antibody molecules present in immune complexes could not be determined. We here describe the production and in vivo use of a monomeric HSA-HRP antigen-enzyme conjugate, readily demonstrable in cryostat sections and ELISA.

Follicular dendritic cell-B cell interactions in virus disease. Common localization but different cell damage caused by antibody immobilized virus?

Follicular dendritic cells (FDC) are involved in the trapping and retention of antigen-antibody complexes in lymphoid follicles. This FDC immobilized antigen is thought to be involved in the generation of memory B-lymphocytes. Follicular trapping of both Aleutian disease virus and HIV particles has been demonstrated.

The immune response in the rat to Streptococcus pneumoniae type 3 and type 4 capsular polysaccharide. Detection by double immunocytochemical staining of antibody-containing cells in situ and ELISA.

Two different methods have been used to study immune responses in the rat to Streptococcus pneumoniae type 3 and type 4 capsular polysaccharides (PPS). First, for simultaneous detection of the specificity and isotype of anti-PPS antibody-containing cells (ACC) in cryostat sections of lymphoid tissue, a double immunocytochemical method was developed. This method is a combination of a three-step immunoperoxidase method to demonstrate specific anti-PPS ACC as bright red cells and a two-step immunophosphatase method to detect the isotype of ACC as blue cells.

Chronic inflammation induces the expression of dendritic cell markers not related to functional antigen presentation on peritoneal exudate macrophages.

Phenotypic heterogeneity between macrophages in situ has been reported, using different macrophage-specific monoclonal antibodies. Microenvironmental factors, which may play an important role in inducing this heterogeneity were studied in a local inflammatory response in vivo. Our results show that peritoneal exudate macrophages, formed during Thioglycollate induced chronic inflammation, acquire expression of the dendritic cell markers NLDC-145 and 6D2.

Development of antibody-forming cells in follicles of lymph nodes of mice after continuous antigenic stimulation.

It was the purpose of the present study to test a hypothesis on the direct differentiation of newly formed memory B cells into antibody-forming cells (AFC) in the follicles of lymph nodes. AFC may develop in follicles when mobile antigen is present at the moment that such memory B cells have completed their differentiation under influence of immune complexes trapped on follicular dendritic cells (FDC). In order to study whether the simultaneous presence of mobile antigen and immobilized immune complexes on FDC alters the normal distribution of AFC in lymph nodes, different immunization protocols with the thymus-dependent antigens trinitrophenylated keyhole limpet haemocyanin (TNP-KLH) and horseradish peroxidase (HRP) were used.

Kupffer cell depletion in vivo results in preferential elimination of IgG aggregates and immune complexes via specific Fc receptors on rat liver endothelial cells.

In the present study we have investigated the clearance kinetics and tissue distribution of monomeric (m) IgG and soluble aggregates of IgG (AIgG) and immune complexes (IC) in normal and Kupffer cell (KC) depleted rats. In normal rats, clearance of mIgG occurred in a biphasic manner with a first half-life (T1/2) (T1) of 36.3 +/- 6.

The in situ immune response of the rat after intraperitoneal depletion of macrophages by liposome-encapsulated dichloromethylene diphosphonate.

This study concerns the contribution of peritoneal macrophages in vivo to local and systemic immune responses in the rat. Peritoneal macrophages as well as macrophages in the draining parathymic lymph nodes were selectively eliminated by intraperitoneal inoculation of dichloromethylene-diphosphonate-containing liposomes. This depletion resulted in an enhanced immune reaction to intraperitoneally administered trinitrophenyl keyhole limpet haemocyanin in the parathymic lymph nodes, as demonstrated by the higher numbers of specific anti-TNP antibody-forming cells in macrophage-depleted animals than in control animals from day 5 after immunization.

Kupffer cell depletion in vivo results in clearance of large-sized IgA aggregates in rats by liver endothelial cells.

We investigated the clearance kinetics and tissue distribution of different sized IgA in normal and macrophage-depleted rats. Rats were injected iv with liposomes containing dichloromethylene diphosphonate (DMDP). DMDP treatment resulted in complete depletion of liver macrophages 24-48 h after administration.

Selective depletion of macrophages prevents pituitary-adrenal activation in response to subpyrogenic, but not to pyrogenic, doses of bacterial endotoxin in rats.

The mechanisms by which bacterial endotoxin [lipopolysaccharide (LPS)] stimulates the hypothalamo-pituitary-adrenal axis (HPAA) have not been elucidated. The present study was designed to investigate the involvement of macrophages in plasma ACTH and corticosterone responses to LPS administration in rats using selective in vivo macrophage depletion. Intraperitoneal administration of subpyrogenic doses of LPS to normal rats resulted in elevated plasma ACTH and corticosterone concentrations, measured 2 h later.

Selective depletion of liver and splenic macrophages using liposomes encapsulating the drug dichloromethylene diphosphonate: effects on antimicrobial resistance.

The current results provide direct evidence for a role of tissue macrophages (M phi) in natural immunity and support the use of immunomodulators to enhance antiviral resistance in immunocompromised individuals. In this study, macrophages (M phi) in the spleen and liver were eliminated by intravenous (i.v.

Effects of clodronate and pamidronate on splenic and hepatic phagocytic cells of mice.

Bisphosphonates inhibit the activity of osteoclasts and conceivably also macrophage activity. Administered in hypoosmotic solution, clodronate (dichloromethylene bisphosphonate) forms complexes with the iron of haemolysed erythrocytes and subsequently accumulates in splenic and hepatic macrophages. Pamidronate (3-amino-1-hydroxypropylidene bisphosphonate) also accumulates in the spleen and liver of mice and rats even when injected in isoosmotic solution.

Elimination of spleen and of lymph node macrophages and its difference in the effect on the immune response to particulate antigens.

To study the role of macrophages in the in situ immune response to particulate antigens in spleen and popliteal lymph nodes (PLN), mice were injected with dichloromethylene diphosphonate (Cl2MDP)-containing liposomes to eliminate macrophages, followed by immunization with trinitrophenylated sheep red blood cells (TNP-SRBC). Depletion of macrophages in the spleen caused a strong decrease in the number of antibody-forming cells (AFC), which develop after intravenous (i.v.

Antigen processing and presentation in vivo: the microenvironment as a crucial factor.

Antigen processing and presentation in vitro is an increasingly well understood phenomenon. However, in vivo, a large number of variables conspire to obscure and confuse. In this article, Nico van Rooijen attempts to bring order to events that occur in the spleen after antigenic challenge: starting with the large body of reliable in vitro data he incorporates information on splenic anatomy, cell trafficking and the cellular microenvironment to arrive at a physiological model for antigen handling in vivo.