Recognition of heterologous cells by macrophages. I. Species recognition by mouse and guinea pig macrophages in the phagocytosis of heterologous thymocytes

Comparison of fluorescence-based methods to determine nanoparticle uptake by phagocytes and non-phagocytic cells in vitro

At many portals of entry the relative uptake by phagocytes and non-phagocytic cells has a prominent effect on availability and biological action of nanoparticles (NPs). Cellular uptake can be determined for fluorescence-labeled NPs. The present study compares three methods (plate reader, flow cytometry and image analysis) in order to investigate the influence of particle size and functionalization and medium content on cellular uptake of fluorescence–labeled polystyrene particles and to study the respective method’s suitability for uptake studies. For comparison between the techniques, ratios of macrophage to alveolar epithelial cell uptakes were used. Presence of serum protein in the exposure solution decreased uptake of carboxyl-functionalized and non-functionalized particles; there was no clear effect for the amine-functionalized particles. The 200 nm non- or carboxyl-functionalized NPs were taken up preferentially by phagocytes while for amine-functionalized particles preference was lowest. The presence of the serum slightly increased the preference for these particles.

In conclusion, due to the possibility of calibration, plate reader measurements might present a better option than the other techniques to (semi)quantify differences between phagocytes and non-phagocytic cells for particles with different fluorescence. In order to obtain unbiased data the fluorescent labeling has to fulfill certain requirements.

Modifications of the immune response induced by Histoplasma capsulatum products

To understand the host-parasite relationship in histoplasmosis, mice were inoculated with histoplasmin (HP), the filtrate of aged cultures of Histoplasma capsulatum, and the immune response of these mice towards sheep red blood cells (SRBC) and to trinitrophenyl hapten was studied. The filtrate abrogated completely the primary antibody response to both antigens as measured by the number of spleen hemolytic plaque forming cells when HP was administered at doses greater than 200 micrograms two days before the antigen. Suppression was elicited by HP when it was injected either intravenously, intraperitoneally, or subcutaneously. Inoculation with HP and antigen on the same day did not result in suppression. The secondary antibody response was not modified at any dose. Variation of the response with time was determined by counting the number of rosette forming cells (RFC) to SRBC every two days for a total of 21 days. Antibody-mediated RFC ('B' rosettes) were depressed throughout the experiment, while the number of non 'B', presumably T, RFC did not vary from control values. In animals inoculated with HP alone, high number of RFC were detected on day 11 after HP inoculation, suggesting that HP may have polyclonal activation effects. These results support the possibility that H. capsulatum evades the immune defenses by induction of a suppressive phenomenon in which the afferent limb of the immune response is not involved. This effect appeared to be induced directly by a product of the fungus, instead of by factors generated during the immune response to this microorganism.

Phagocytosis of unopsonized zymosan particles by trypsin-sensitive and beta-glucan-inhibitable receptors on bone marrow-derived murine macrophages

Murine bone marrow cells, plated at 4 X 10(4) cells/well and cultured in 50% fibroblast CM, yielded pure populations of large, individual, adherent cells that were phagocytic and morphologically indistinguishable from macrophages. Adherent macrophages appeared in small numbers with 24 h of culture, increased to maximal cell numbers within 10 days of culture, and remained at these cell densities for at least 11 weeks in culture. The capacities of adherent macrophages to ingest unopsonized zymosan particles and EsIgG, at inputs of 1.25 X 10(7) targets, were expressed by 7 and 40% of the cells derived from 24-hour cultures, respectively, were increased at nearly identical rates to comparable maximal levels within 10-14 days of culture and were exhibited by essentially all adherent cells derived from 2-11-week cultures. The percentage of adherent macrophages from twelve 3-6-week cultures ingesting greater than or equal to 1, greater than or equal to 6 and greater than or equal to 10 zymosan particles was 89 +/- 5, 47 +/- 11 and 14 +/- 9% (mean +/- SD, n = 12), respectively, and the percentage ingesting greater than or equal to 1, greater than or equal 6 and greater than or equal to 10 EsIgG was 86 +/- 5, 49 +/- 10 and 14 +/- 8%, respectively. Incubation of adherent macrophages with mannan-free ss-glucan particles at inputs of 5 X 10(5)-5 X 10(7)/ml initiated a phagocytic response comparable to that obtained with the same doses of zymosan particles which contained mannan and beta-glucan. Preincubation of adherent macrophages with 100 micrograms/ml of a fully soluble beta-glucan, laminarin, and solubilized barley beta-glucan reduced subsequent macrophage phagocytosis of greater than or equal to 6 zymosan particles by 53 and 40%, respectively. In contrast, yeast alpha-mannan was less than 1% as active, and 10 mg/ml reduced the number of adherent macrophages ingesting greater than or equal to 1 zymosan particles by 64%. At concentrations as high as 2 mg/ml, laminarin and barley beta-glucan had no effect on Fc receptor-mediated ingestion of EsIgG, and mannan at 20 mg/ml also failed to inhibit EsIgG ingestion. Pretreatment of adherent macrophages with 20 micrograms/ml of trypsin reduced the number of cells ingesting greater than or equal to 1 zymosan particles from 89 to 10% and those ingesting greater than or equal to 6 zymosan from 43 to 0%, whereas pretreatment with as much as 100 micrograms/ml of trypsin failed to decrease macrophage ingestion of EsIgG.(ABSTRACT TRUNCATED AT 400 WORDS)

Interaction of macrophages and lymphocytes in rat skin allografts

Light microscopy of 2 microgram sections of rejecting rat skin allografts, embedded in hydroxyethyl methacrylate, revealed among the cells infiltrating the graft base extravascular macrophages containing a small lymphocyte. Toluidine blue staining indicated DNA degradation in some of these phagocytosed lymphocytes. More frequently small lymphocytes were in intimate contact with the surface of the macrophages, resembling "Periopolesis', which others have previously observed in vitro. These macrophage-lymphocyte interactions were not seen in sections of autografts. Despite a previous report that diphenylhydantoin (phenytoin) impairs macrophage function, these macrophage-lymphocyte interactions were present in grafts placed in rats receiving this drug. This treatment did not hasten or delay the onset of graft rejection. These in vivo findings both accord with recent in vitro studies on the mechanisms of phagocytosis and with reports that phagocytosis is one of the effector mechanisms in allograft rejection. However, macrophage phagocytosis of lymphocytes has also been observed in testicular lymph collected from conscious normal sheep.

Recognition of heterologous cells by macrophages. II. The mechanism of phagocytosis of chicken thymocytes by mouse and guinea pig macrophages

Mouse and guinea pig macrophages cultured in vitro actively phagocytize non-opsonized thymocytes from certain heterologous animals including chickens, as shown in the accompanying paper (11). The present study was undertaken to investigate the mechanism of this phenomenon, using the phagocytosis of chicken thymocytes (c-thymocytes) by mouse and guinea pig macrophages. The involvement in this phenomenon of natural IgG passively adsorbed in situ to macrophages was excluded, since the phagocytosis of c-thymocytes was not significantly affected by the treatment of macrophages with homologous IgG or rabbit anti-sera directed toward homologous IgG. The involvement of lectin- or sugar-like receptors seems also to be unlikely, since various glycoproteins showed no significant effect. c-Thymocytes treated with normal mouse serum (NMS) but not with heat-inactivated NMS were strongly stained with goat anti-mouse C3 by an indirect immunofluorescent technique, and became extremely vulnerable to adherence to and phagocytosis by mouse macrophages, suggesting that c-thymocytes are an activator of the alternative pathway of mouse complement. These results as a whole raise the possibility that mouse and guinea pig macrophages can phagocytize c-thymocytes by recognizing their activating surfaces of the alternative complement pathway without the participation of exogenously added IgG or complement, as proposed by others in the phagocytosis of rabbit and mouse red blood cells by human monocytes.