Effect of protein A on mast cell numbers and macrophage phagocytic activity

Enhanced macrophage antitumor effects of protein A in combination with IFN-gamma

In this study we examined the potential for the synergistic augmentation of the antitumor activity of inflammatory mouse peritoneal macrophages by stimulation with protein A combined with IFN-gamma. The moderate augmentative effect induced by preincubation with protein A was demonstrated to be concentration-dependent, whereas IFN-gamma had a very low activating effect. Following preincubation with both protein A and IFN-gamma, a marked enhancement of macrophage activity was noted. In addition, based on the utilization of neutralizing antibody to TNF-alpha or the inhibition of NO production, TNF-alpha and NO were proven to be involved as mediators during the activation of tumoricidal macrophages by protein A in combination with IFN-gamma. We also demonstrated that supernatants from macrophages treated with protein A plus IFN-gamma contained both TNF-alpha and NO at markedly increased levels. Thus, tumor cell lysis in the combined system was mediated via TNF-alpha or NO. These results demonstrate the synergistic effects on mouse peritoneal macrophage function of protein A in combination with IFN-gamma and suggest that combinations of such agents may serve as the basis for future in vivo immunotherapy.

Antitumour activity of protein A in a mouse skin model of two-stage carcinogenesis

Protein A (PA) is an immunostimulating glycoprotein (mol. wt. 43,000 kDa) obtained from Staphylococcus aureus cowan I. The antitumour property of PA is well documented in the literature in various transplantable tumours of rats and mice. In the present set of investigations, the antitumour property of PA was tested in Swiss albino mice in a two-stage initiation-promotion mouse skin carcinogenesis model. The animals were initiated topically with a single subcarcinogenic dose (52 microgram) of 7,12-dimethylbenzanthracene (DMBA). PA was administered intraperitoneally (1 microgram/animal), twice weekly for 2 weeks. Promotion was performed by twice weekly applications of 12-O- tetradecanoyl phorbol-13-acetate (TPA) at a dose of 5 microgram/animal for 32 weeks. The result showed that the treatment schedule can effectively check the onset of tumorigenesis, the cumulative number of tumours and the average number of tumours per mouse. In the PA administered group, 30% of the animals remained tumour free until the termination of the experiments (i.e. 32 weeks of promotion). Thus the present study proves that protein A can effectively inhibit DMBA initiated and TPA promoted mouse skin carcinogenesis.

Modulation of primary antibody response by protein A in tumor bearing mice

Protein A (PA) is a cell wall glycoprotein of Staphylococcus aureus Cowan I, which possess a number of immunomodulatory and antitumor properties. We have previously shown that PA suppresses the anti-sheep erythrocyte primary antibody response in normal mice. The present investigation evaluates the effect of protein A on the anti-sheep erythrocyte primary antibody response in tumor-bearing mice. The primary antibody response in tumor-bearing mice immunized with sheep red blood cells (SRBC) was suppressed by the intraperitoneal administration of PA in a dose-dependent fashion. The plaque forming cell (PFC) assay was used to assess this response. Maximum suppression of the PFC response was observed at 12 micrograms PA/animal (p < 0.001) and could be observed at doses as low as 1 microgram PA/animal (p < 0.01). The amount of suppression was proportional to the number of PA doses administered. In addition this effect was critically dependent on the timing of PA administration. PA showed no significant effect on PFC when injected after immunization, but it produced pronounced suppression when injected prior to the immunization with SRBC. Maximum suppression of the PFC response was observed when PA was administered one day before the antigen challenge. PA also reduced splenic localization of 51Cr labeled SRBC to 42% (p < 0.01). The altered localization of antigen in spleen may be responsible for reduced PFC response in tumor-bearing mice. Depletion of B-lymphocyte is reported to exhibit tumor inhibition. Therefore, we propose that the suppression of the primary antibody response by PA helps in tumor regression by reducing the soluble immunosuppressive immune complexes.

Immunostimulating effects of protein A in immunosuppressed aflatoxin-intoxicated rats

Aflatoxin B1, the potent carcinogenic compound produced by the Aspergillus flavus group of fungi on food and feed, induces immunosuppressive effects in rodents. In this communication, we report an immunomodulatory approach to abrogate aflatoxin B1-induced immunotoxicity in rats using protein A of Staphylococcus aureus Cowan 1. We have earlier demonstrated that protein A can protect the animals from toxicities induced by a number of drugs, chemicals and toxins. In the present study various combinations of aflatoxin B1 exposure and protein A treatment in animals were used. It was observed that protein A could provide protection to animals from aflatoxin B1-induced immunotoxicity, as measured by a battery of tests assessing cell-mediated immunity (CMI) profile of the host. Various parameters showing suppression of CMI following aflatoxin B1 exposure were reverted back towards normalcy in protein A-treated animals. It is concluded that protein A may prove to be a useful agent to protect the host from aflatoxin immunotoxicity, in view of its stimulatory effects on various immune functions even after their initial depression due to aflatoxin B1.

Acrylamide induced immunosuppression in rats and its modulation by 6-MFA, an interferon inducer

In the present communication, we describe acrylamide (ACR) induced immunotoxicity and its modulation by an interferon inducer, the 6th mycelial fraction acetone (6-MFA) of Aspergillus ochraceus ATCC 28706. ACR administration to rats produced a significant decrease in the weight of spleen (p < 0.001), thymus (p < 0.001) and mesenteric lymph nodes (p < 0.05). A decrease in cellularity of spleen (p < 0.001), thymus (p < 0.001), bone marrow (p < 0.001) and circulating blood lymphocyte population (p < 0.001) was also recorded. ACR suppressed the humoral as well as cell mediated immunity as assessed by erythrocyte antibody complement (EAC)-rosettes (p < 0.001), hemagglutination titre (p < 0.001), PFC (p < 0.001) and the delayed type hypersensitivity response against sheep red blood cells (SRBC, p < 0.001). ACR treated immunosuppressed rats when treated with 6-MFA restored the circulating lymphocyte number to the normal level and a partial recovery in the weight of spleen and thymus. Potentiation of EAC-rosettes, hemagglutination titre, IgM-PFC and DTH response against SRBC was observed. It is concluded that 6-MFA ameliorate the ACR induced toxicity. This study may be of significance in prevention of ACR toxicity.

Modulation of anti-sheep erythrocyte primary antibody response by protein A in normal mice

Protein A (PA), a cell wall glycoprotein of Staphylococcus aureus Cowan I, is known to possess immunomodulatory and antitumor activities. In the present study the effect of protein A on the anti-sheep erythrocyte primary antibody response in normal mice has been investigated. Intraperitoneal administration of PA resulted in suppression of primary antibody response in mice immunized with sheep red blood cells (SRBC) as assessed by plaque forming cell (PFC) assay. The suppressive effect was dose dependent. Maximum suppression in PFC response was observed at 12 micrograms PA/animal and could be observed as low as 1 microgram PA/animal. The suppression at 6 and 12 micrograms PA/animal was significant when compared with control values (p < 0.02 and p < 0.001, respectively). However, no significant suppression was recorded at 1 microgram dose. The suppression was proportional to the numbers of administrations of PA to the mice and critically dependent on the timing of inoculation of PA. PA produced pronounced suppression when injected prior to the immunization of animals with SRBC. PA reduced splenic localization of 51Cr labelled SRBC to 55%. It is proposed that the altered localization of antigen (SRBC) in spleen may be responsible for reduced plaque forming cells in normal mice.

Mechanism of enhanced phagocytic response in protein a treated rat macrophages

Protein A of S. aureus Cowan I has been shown to stimulate macrophage mediated phagocytosis. The present study was undertaken to understand the mechanism involved in the enhancement of phagocytosis of peritoneal macrophages by protein A. The lucigenin and luminol-dependent chemiluminescence (CL) of rat peritoneal macrophages, after incubation with various concentrations of protein A, flow-cytometric studies using DCFH-DA as a fluorescent compound and phagocytosis of sheep red blood cells (SRBCs) by rat peritoneal macrophages were studied. A significant increase in lucigenin dependent CL due to formation of superoxide anions (O2-.) and in luminol dependent CL due to formation of hydrogen peroxide (H2O2) was observed in protein A treated macrophages. A significant increase in intracellular hydrogen peroxide (H2O2) was also observed along with an increase in phagocytosis of SRBCs by protein A treated macrophages. The present findings indicate that protein A helps to increase phagocytosis and triggers respiratory burst of macrophages. Thus, both increased phagocytic response and respiratory burst of macrophages in protein A treated animals may be contributing to the antitumor property of protein A reported earlier.

Protection against 7,12-dimethylbenzanthracene-induced tumour initiation by protein A in mouse skin

Protein A is an immunostimulating glycoprotein obtained from Staphylococcus aureus Cowan I. Its antitumour activity is proven in various tumour models. Its ability to provide protection against tumour initiation by the chemical carcinogen 7,12-dimethylbenzanthracene (DMBA) has been investigated in the present study using a mouse skin model of two-stage carcinogenesis. Protein A was administered intraperitoneally (1 microgram/animal 20 g body wt.) twice a week for 2 weeks, prior to initiation by DMBA. The promotion was performed by twice weekly applications of 12-O-tetradecanoyl phorbol-13-acetate (TPA) (3 or 5 micrograms/animal in 100 microliters acetone). Protein A provided significant protection to animals from DMBA-induced tumour initiation as was observed by the decrease in cumulative number of tumours, percent of animals developing tumours, number of tumours per animal and rate of tumour growth. Our data indicate that protein A has anticarcinogenic properties.

Effect of zinc on immune functions and host resistance against infection and tumor challenge

The effect of zinc treatment on immune function and resistance against infection and tumor challenge was studied in mice. Swiss albino mice were treated with zinc acetate (3 mg/kg body weight) in one or two intraperitoneal injections. Various immune function assays were performed in treated animals. Zinc treatment to normal animals caused potentiation of T-lymphocyte and macrophage functions. Zinc treatment was also found to increase host resistance against Candida albicans and Semliki Forest virus infections. Increased resistance against endotoxin shock and Ehrlich's ascites tumor challenge was also observed in zinc treated animals. It can be stated from this study that zinc treatment potentiates the cell mediated immunity and host resistance against infection and tumor challenge.

Effect of subchronic aflatoxin exposure on growth and progression of Ehrlich's ascites tumor in mice

The present investigation was undertaken to assess whether aflatoxin B1 (AFB1) has any modulatory effect on the growth and progression of Ehrlich's ascites tumor (EAT) in mice or not. Male Swiss albino mice were treated with 0, 70, 350 and 700 micrograms AFB1/kg body weight in 0.2 ml corn oil on alternate days, orally, for two weeks. Treated animals were challenged with 1 x 10(6) cells of Ehrlich's ascites tumor. Animals were monitored for the appearance of palpable tumor, body weight gain as a measure of tumor burden, mortality profile and tumor cell population. Some parameters of cell mediated immunity (CMI), humoral immunity and non-specific immunity were also studied in aflatoxin treated animals in order to find out the mechanism of action of AFB1 on host immunity. It was observed that AFB1 treatment resulted in an early appearance of tumor, enhanced mortality, appreciable increase in body weight gain and EAT cell population following tumor challenge, in comparison with the control animals. Aflatoxin treatment caused suppression of CMI including an impairment of macrophage function, while humoral immunity was not much affected. It may be concluded that impaired CMI and macrophage function might be contributing to the increased growth of EAT in the AFB1 treated animals. Our findings may be relevant in that when a host is exposed to aflatoxins concomitantly with other carcinogens and cancer causing situations.

Effects of aflatoxin on lymphoid cells of weanling rat

Aflatoxin (AF), the hepatocarcinogenic food contaminant produced by the Aspergillus flavus group of fungi, is known to interact with various vital processes, including the immune function. Effects of long-term treatment of three dose levels of aflatoxin B1 (AFB1) on lymphoid cells of weanling rats were studied. AFB1 treatment caused a reduction in body weight gain, significantly (P less than 0.01) at the 700 microgram level. There was also a significant decrease in the weight of spleen and thymus in AFB1-treated animals in comparison to control. Similarly, AFB1 depleted cell populations of thymus and bone marrow and WBC and RBC counts. There was a marked reduction in the population and phagocytic capacity of macrophages due to AFB1 administration at dose levels of 350 and 700 micrograms kg-1 body weight. Macromolecular synthesis of DNA, RNA and protein in macrophages was affected, as there was significant inhibition in the incorporation of [3H]-thymidine, [3H]-uridine and [3H]-leucine. The hampered functioning of macrophages may be due to the cytotoxic action of AFB1.

Protection against carbon-tetrachloride-induced lymphoid organotoxicity in rats by protein A

In a previous study we described protection of rats from carbon tetrachloride (CCl4)-induced hepatotoxicity by protein A (PA). In the present report we described protection against CCl4-induced lymphoid organotoxicity in rats by PA. Our data indicate that CCl4 administration produced a significant increase in the number of total leukocytes and polymorphs in blood, a significant decrease in leukocyte count in bone marrow, and a significant loss in weight of spleen and adrenals. In the animals receiving PA prior to and after CCl4, these values were found to be near those of controls. Histological examination revealed thymocyte depletion in thymic lobe and degenerative changes of tissue in spleen of CCl4-exposed animals. PA treatment to CCl4-exposed animals exhibited improvement and recovery from the damage caused by CCl4. These observations throw a new light on the field of CCl4 toxicity to lymphoid organs and their protection by PA.

Protein A induced abrogation of cyclophosphamide toxicity is associated with concomitant potentiation of immune function of host

This report confirms our previous observation that protein A (PA) of Staphylococcus aureus Cowan I reduces the cyclophosphamide (Cy) induced toxicity. PA treated animals recover quickly from the toxic effects of Cy. We have exhaustively studied the role of specific and nonspecific immunity in the protection of the animals. It was observed that PA helped the animals in the accelerated regeneration of leukocytes of blood (p less than 0.001) and different lymphoid organs like thymus (p less than 0.001), spleen (p less than 0.01) and bone marrow (p less than 0.01). Increased number and function of macrophages was also observed in PA (p less than 0.001) and PA+Cy (p less than 0.001) groups. PA, on one hand enhanced the cell mediated immunity while suppressed the humoral immunity as was assessed by increase in delayed type hypersensitivity response (p less than 0.001) and decreased in plaque forming cells (p less than 0.001), EAC-rosettes (p less than 0.001), hemagglutination (p less than 0.001) and hemolysin titre (p less than 0.05). On the basis of above observations we propose that the immunomodulatory activity of PA helped the animals to remain alive in two ways- (1) by early generation of the cells depleted by the Cy thus helping animals to repair the damaged immune system and fast clearance of the toxic metabolites of Cy (2) by temporarily suppressing the cells responsible for humoral immunity which are more susceptible to Cy metabolites.

Protection against carbon tetrachloride-induced hepatotoxicity by protein A

Protection from carbon tetrachloride (CCL4)-induced hepatotoxicity by protein A was assessed histologically in rats. Carbon tetrachloride exposure produced swollen, vacuolated and necrotic cells in the centrilobular region of the hepatocyte in rats. Animals given protein A prior to and during CCL1 treatment showed a complete absence of hepatic lesions. Our study showed that protein A, a potent immunomodulator, has the potential to reduce liver injury caused by carbon tetrachloride, a known hepatotoxin in the rat.

Increased macrophage activity in protein A treated tumor regressed animals

Male swiss albino mice transplanted with 1 x 10(6) viable fibrosarcoma tumor cells were treated with Protein A (60 micrograms/kg) right from the day of transplantation for 4 weeks, twice weekly. The therapy resulted in lesser tumor incidence, significant inhibition of tumor growth and enhanced percent survival in treated animals as compared to untreated controls. Treated animals also showed gains in body weight, an increase in peripheral blood leucocyte count, significant increase in macrophage function and number. Stimulation of macrophage number and macrophage function by Protein A may be related to its antitumor.