Phagocytic and candidacidal activities of macrophages from suckling and adult mice pretreated with concanavalin-A

Concanavalin-A stimulates IL-17 and nitric oxide production and induces macrophage polarization and resistance to Trypanosoma cruzi infection

AIMS

Chagas disease is a neglected tropical disease. The ability of Trypanosoma cruzi to survive within phagocytes is likely a critical factor for T. cruzi dissemination in the host. For control of the parasite load and host survival, macrophage action is required. Concanavalin-A (Con-A) presents properties that modulate immune functions and protect hosts from several experimental infectious diseases. Here, we evaluated the effects of Con-A on peritoneal macrophages as well as on the course of experimental infection by T. cruzi.

MAIN METHODS

BALB/c mice, a susceptible model for T. cruzi infection, were treated with Con-A via the intraperitoneal route and 3 days later infected with T. cruzi. We quantified parasitemia, cytokines and nitric oxide (NO). Peritoneal exudate and macrophages were collected for macrophage phenotyping and cell viability, NO and cytokine detection, as well as for T. cruzi internalization and release index determination.

KEY FINDINGS

Con-A treatment induced IL-17a and NO production by cells from the peritoneal cavity, and M1 marker expression predominated on peritoneal macrophages. These cells are also more prone to producing TNF-α, IL-6 and NO when infected by T. cruzi and show high trypanocidal capacity. Due to a hostile peritoneal microenvironment caused by Con-A, which induces macrophage cNOS and iNOS expression, infected BALB/c mice showed reduced parasitemia and an increased survival rate.

SIGNIFICANCE

We conclude that Con-A can induce peritoneal M1 macrophage polarization to increase trypanocidal activity, resulting in ameliorated systemic infection in a susceptible experimental model.

Structure-function and application of plant lectins in disease biology and immunity

Lectins are proteins with a high degree of stereospecificity to recognize various sugar structures and form reversible linkages upon interaction with glyco-conjugate complexes. These are abundantly found in plants, animals and many other species and are known to agglutinate various blood groups of erythrocytes. Further, due to the unique carbohydrate recognition property, lectins have been extensively used in many biological functions that make use of protein-carbohydrate recognition like detection, isolation and characterization of glycoconjugates, histochemistry of cells and tissues, tumor cell recognition and many more. In this review, we have summarized the immunomodulatory effects of plant lectins and their effects against diseases, including antimicrobial action. We found that many plant lectins mediate its microbicidal activity by triggering host immune responses that result in the release of several cytokines followed by activation of effector mechanism. Moreover, certain lectins also enhance the phagocytic activity of macrophages during microbial infections. Lectins along with heat killed microbes can act as vaccine to provide long term protection from deadly microbes. Hence, lectin based therapy can be used as a better substitute to fight microbial diseases efficiently in future.

Modelling the host-pathogen interactions of macrophages and Candida albicans using Game Theory and dynamic optimization

The release of fungal cells following macrophage phagocytosis, called non-lytic expulsion, is reported for several fungal pathogens. On one hand, non-lytic expulsion may benefit the fungus in escaping the microbicidal environment of the phagosome. On the other hand, the macrophage could profit in terms of avoiding its own lysis and being able to undergo proliferation. To analyse the causes of non-lytic expulsion and the relevance of macrophage proliferation in the macrophage–Candida albicans interaction, we employ Evolutionary Game Theory and dynamic optimization in a sequential manner. We establish a game-theoretical model describing the different strategies of the two players after phagocytosis. Depending on the parameter values, we find four different Nash equilibria and determine the influence of the systems state of the host upon the game. As our Nash equilibria are a direct consequence of the model parameterization, we can depict several biological scenarios. A parameter region, where the host response is robust against the fungal infection, is determined. We further apply dynamic optimization to analyse whether macrophage mitosis is relevant in the host–pathogen interaction of macrophages and C. albicans. For this, we study the population dynamics of the macrophage–C. albicans interactions and the corresponding optimal controls for the macrophages, indicating the best macrophage strategy of switching from proliferation to attacking fungal cells.

Targeting the Immune System with Plant Lectins to Combat Microbial Infections

The arsenal of drugs available to treat infections caused by eukaryotic and prokaryotic microbes has been declining exponentially due to antimicrobial resistance phenomenon, leading to an urgent need to develop new therapeutic strategies. Host-directed immunotherapy has been reported as an attractive option to treat microbial infections. It consists in the improvement of host defenses by increasing the expression of inflammatory mediators and/or controlling of inflammation-induced tissue injury. Although the in vitro antimicrobial and immunomodulatory activities of lectins have been extensively demonstrated, few studies have evaluated their in vivo effects on experimental models of infections. This review aims to highlight the experimental use of immunomodulatory plant lectins to improve the host immune response against microbial infections. Lectins have been used in vivo both prophylactically and therapeutically resulting in the increased survival of mice under microbial challenge. Other studies successfully demonstrated that lectins could be used in combination with parasite antigens in order to induce a more efficient immunization. Therefore, these plant lectins represent new candidates for management of microbial infections. Furthermore, immunotherapeutic studies have improved our knowledge about the mechanisms involved in host–pathogen interactions, and may also help in the discovery of new drug targets.

Infection and tissue repair of experimental cutaneous candidiasis in diabetic mice

PURPOSE

Diabetic patients seem to be predisposed to cutaneous candidiasis. In this study, we evaluated the interference of diabetic conditions in alloxan-induced diabetic mice in relation to the development of C. albicans infection, density of M1 and M2 macrophages, distribution of collagen type I and III and anti-inflamamatory cytokines involved in tissue repair.

METHODOLOGY

The mice were treated with intravenous alloxan, and all animals with blood glucose levels >250  mg dl-1 were inoculate with C. albicans intradermally in the hind paw and were studied for up to 21 days. Control groups without alloxan were used. The fungal burden was evaluated by periodic acid-Schiff (PAS) and by counting the colony forming units. Total population of macrophages were targeted with antibody to F4/80 antigen and M2 macrophages with anti-arginase antibody. Anti-inflammatory cytokines from popliteal lymph nodes were determined by capture ELISA procedures. Picrosirius red staining allowed qunantification of collagen types I and III in the infected skin by using a polarized light microscope.Results/Key findings. Diabetic mice, versus non-diabetic mice, showed a significant lower density of F4/80 and M2 macrophages, higher fungal burden, deficiency in interleukin (IL)-4 production, and delayed IL-13 responses. The later clearance of C. albicans enhanced tissue injury, leading to a decrease in collagen type I. Moreover, collagen type III was increased by interference of IL-13 and transforming growth factor-β cytokines.

CONCLUSION

These findings highlight some important changes in diabetic animal responses to C. albicans infection that may be important to the pathophysiological processes underpinning cutaneous candidiasis in diabetic patients.

Protective effect of Artin M from extract of Artocarpus integrifolia seeds by Th1 and Th17 immune response on the course of infection by Candida albicans

The immunoregulatory effect of Artin M and jacalin from extract of Artocarpus integrifolia seeds (jack extract) against infection with Candida albicans was investigated. Swiss mice received jack extract containing 500 μg protein/ml PBS intraperitoneally (i.p.) or PBS alone and after 72 h were infected i.p. with C. albicans CR15 (10(7)) and sacrificed after 30 min, 2, 6, 24, and 72 h. ELISA analysis revealed that in jack extract-treated mice IFN-γ was predominantly produced versus IL-10 in control mice. These results suggest that jack extract induced a protective immune response, since C. albicans clearance was complete at 72 h postinfection. Jack extract presents two lectins (Artin M and jacalin) with distinct biological properties. Artin M was able to induce IL-12 production by macrophages. Also, Artin M in different concentrations, associated with jacalin or in jack extract induced both IFN-γ and IL-17 production. As a consequence, phagocytic and candidacidal activity increased significantly. Alanine aminotransferase activity (ALT) was used as parameter for damage of the liver. The activity of ALT correlated with inoculum size that increased significantly in control group, however, mice pretreated with jack extract 3 days before infection presented normal ALT. Mice pretreated with jack extract that received a lethal inoculum of Candida presented 90% survival versus 20% among controls or mice pretreated with jacalin. Thus, the results suggest that Artin M by itself, associated with jacalin or present in jack extract is able to induce protective Th1 and Th17 immune responses against Candida albicans infection.

Concanavalin A protects mice from a lethal inoculation of intragastric Klebsiella pneumoniae and reduces the induced liver damage

Intragastric inoculation of Klebsiella pneumoniae can cause invasive diseases, including necrosis of liver tissues and bacteremia. The effect of concanavalin A (ConA) on K. pneumoniae was tested. Pretreatment with ConA was able to protect mice from K. pneumoniae infection in an intragastric model. K. pneumoniae-induced mouse death and liver injury such as liver necrosis, as well as blood levels of aspartate aminotransferase and alanine aminotransferase, were inhibited in a dose-dependent manner by ConA. ConA administered intravenously as late as 24 h after K. pneumoniae inoculation was still protective. In an in vitro assay, ConA was able to bind K. pneumoniae cells directly and further agglutinate them but had no effect on their in vitro growth. Surveys of bacterial counts of ConA-treated mice revealed that the bacteria were eliminated effectively in both blood and liver tissues. Furthermore, the bactericidal activity of macrophages against K. pneumoniae was also enhanced in a dose-dependent manner by ConA in an in vitro culture. These data suggest that ConA is a potentially therapeutic agent for K. pneumoniae-induced liver infection.

Low dose of Concanavalin-A enhances innate immune response and prevents liver injury in mice infected withCandida albicans

The mechanisms through which Candida albicans is recognized by immune cells and how it triggers host defence are not completely understood. In this study, we evaluated the effect of Concanavalin-A on the clearance of C. albicans by infected mice and their production of proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha). Subgroups of 5 animals were pretreated with Con-A (250 mug mL(-1) PBS) and after 96 h were infected intraperitoneally with 10(7) cells of C. albicans CR15 (an isolate from a HIV+ person); 30 min, 2, 6, 24 or 72 h after infection the mice were sacrificed. Phagocytosis of C. albicans by peritoneal macrophages increased 30 min after infection in mice pretreated with Con-A. The liver presented the greatest number of CFUs, and this number was reduced by pretreatment with Con-A. Control animals infected with C. albicans presented a significant increase in plasmatic alanine aminotransferase, which was not observed in mice treated with Con-A. Two hours after infection the production of TNF-alpha in the liver of mice pretreated with Con-A was significantly increased. These results suggest that a single dose of Con-A caused a beneficial modulating action of the inflammatory response during infection with C. albicans.

Concanavalin A enhances phagocytosis and killing of Candida albicans by mice peritoneal neutrophils and macrophages

In this study we tested the hypothesis that after administration of a single intraperitoneal dose of concanavalin A (Con-A) to mice, the proportion of neutrophils and macrophages in the peritoneal exudate and their phagocytic and candidacidal activities should change with time. The number of neutrophils in the peritoneal exudate was greatly increased 6 h after administration of Con-A, and those cells were able to kill both intracellular and extracellular yeast and germ tube forms of Candida albicans. Addition of catalase to the culture medium reduced the killing of C. albicans, suggesting that the candidacidal activity depended on the myeloperoxidase system. The survival of mice pretreated with Con-A and submitted to an inoculum of C. albicans 6 h afterwards was twice higher than that of controls, which suggests that neutrophils were able to clear the experimental infection. One day after the treatment, the population of neutrophils in the exudate was about 45%, but after 2 days it was reduced to only 5% and the candidacidal activity was also reduced. After 4 days the exudate contained over 95% of macrophages, the candidacidal activity reached a maximum, and the phagocytosis mediated by both complement receptors and mannose receptors was increased. Uptake of FITC-mannose-BSA by macrophages was maximal on about the 4th day and was inhibited by mannan, suggesting that treatment with Con-A increased the activity of mannose receptors. These results support the hypothesis that activation of cellular immunity by Con-A occurred in two phases, one dominated by neutrophils, and the other by macrophages expressing increased activity of mannose receptors.