Rosa Adriana Jarillo-Luna

Entamoeba histolytica: immunohistochemical study of hepatic amoebiasis in mouse. Neutrophils and nitric oxide as possible factors of resistance.

Studies in mice have not rendered conclusive data on cell and humoral factors to support the resistance of this rodent to Entamoeba histolytica infection. In Balb/c and C3H/HeJ mice inoculated with live or fixed trophozoites, we studied the evolution of the hepatic lesion, the kinetics of inflammatory cells, and the participation of some humoral factors in the development of the hepatic amoebic lesion. From the first hour, amoebae were surrounded by neutrophils containing inducible nitric oxide synthase (iNOS); macrophages also expressing iNOS appeared lately, whereas NK cells were not part of the inflammatory infiltrates. On the fourth day, neutrophils, macrophages, T and B lymphocytes, plasma cells, and some NK cells limited the lesions and anti-amoeba antibodies appeared when most parasites had been eliminated. Therefore, the resistance of the mice to E. histolytica probably lies in non-specific immune responses, among which the activation of neutrophils and the production of nitric oxide (NO) may be important amoebicide factors.

Hypophysectomy and neurointermediate pituitary lobectomy reduce serum immunoglobulin M (IgM) and IgG and intestinal IgA responses to Salmonella enterica serovar Typhimurium infection in rats.

ABSTRACT The influence of anterior pituitary hormones on the gastrointestinal tract of humans and animals has been reported. Hypophysectomy (HYPOX) in the rat causes atrophy of the intestinal mucosa, reduction of gastric secretion and intestinal absorption, and increased susceptibility to infections. To our knowledge, there are no studies on the humoral immune response of the gut-associated lymphoid tissue after HYPOX. We have reported that decreased secretion of vasopressin and oxytocin due to neurointermediate pituitary lobectomy (NIL) diminishes humoral and cell-mediated immune responses. However, no data have been published on whether NIL can affect intestinal immune responses. We analyzed the effects of HYPOX and NIL on bacterial colonization of the intestinal lumen, Peyers patches, and spleen as well as the serum immunoglobulin G (IgG) and IgM and specific intestinal IgA levels in response to Salmonella enterica serovar Typhimurium oral infection. Results showed the following: (i) Salmonella serovar Typhimurium was eliminated from the intestinal lumen at the same rate in rats that underwent a sham operation, HYPOX, and NIL; (ii) Salmonella serovar Typhimurium colonization of Peyers patches and spleen was significantly higher in both HYPOX and NIL rats than in sham-operated rats; (iii) serum IgG and IgM and intestinal IgA against surface proteins of Salmonella serovar Typhimurium were significantly lower in HYPOX and NIL rats than in sham-operated rats; and (iv) compared to NIL rats, higher Peyers patch and spleen bacterial colonization and decreased IgG, IgM, and IgA production were observed in HYPOX rats. We conclude that hormones from each pituitary lobe affect the systemic and gastrointestinal humoral immune responses through different mechanisms.

Diet, exercise and gut mucosal immunity.

Diet and exercise are primary strategies recommended for the control of the obesity epidemic. Considerable attention is being paid to the effect of both on the immune system. However, little research has been done on the effect of diet, nutrients or exercise on the mucosal immune system. The gastrointestinal tract (gut) is not only responsible for the entry of nutrients into the organism, but also for triggering the primary immune response to orally ingested antigens. The gut-associated lymphoid tissue contains a large amount of immune cells, disseminated all along the intestine in Peyers patches and lamina propria. Specific nutrients or their combinations, as well as the microflora, are capable of modulating the immune system through cell activation, production of signalling molecules or gene expression. We have observed an increase in T-cells as well as a decrease in B-cells from Peyers patches, induced by diets high in fats or carbohydrates in Balb/c mice. It has also been demonstrated that exercise modulates the immune system, where moderate levels may improve its function by increasing the proliferation of lymphocytes from various sites, including gut-associated lymphoid tissue, whereas exhaustive acute exercise may cause immunosuppression. High-fat diets combined with exercise are able to induce an increase in CD3+ lymphocytes due to increased CD8+ cells and a decrease in B-cells. Explanations and consequences of the effects of diet and exercise on the gut mucosal immunity are still being explored.

Hypophysectomy and neurointermediate pituitary lobectomy decrease humoral immune responses to T-independent and T-dependent antigens

In rats, hypophysectomy (HYPOX) or neurointermediate pituitary lobectomy (NIL) reduce humoral and cell-mediated immune responses. However, to our knowledge, the differences in the effects of anterior versus posterior pituitary hormones on the immune responses have not been studied to date. We compared in rats, the effects of sham surgery (SHAM), HYPOX, and NIL on humoral immune responses to T cell-independent (TI) type 1 antigen DNP-LPS and to TI type 2 antigen DNP-FICOLL, as well as to T cell-dependent (TD) antigens ovalbumin (OVA) and bovine serum albumin (BSA). The results showed that: (1) both HYPOX and NIL induced a similar and significant decrease in IgM responses towards TI-1 antigens, (2) NIL but not HYPOX induced a decreased IgM response to TI-2 antigens, and (3) both HYPOX and NIL induced similar and significant decrease in IgG responses to TI-2 antigens. Compared with the SHAM group, IgM responses to both TD antigens did not change in HYPOX and NIL animals, whereas the IgG responses to OVA and BSA significantly decreased in HYPOX and NIL animals. These results indicate that hormones of the anterior and posterior pituitary play their own role in the regulation of humoral immune responses.

Peroxynitrite and Peroxiredoxin in the Pathogenesis of Experimental Amebic Liver Abscess

The molecular mechanisms by which Entamoeba histolytica causes amebic liver abscess (ALA) are still not fully understood. Amebic mechanisms of adherence and cytotoxic activity are pivotal for amebic survival but apparently do not directly cause liver abscess. Abundant evidence indicates that chronic inflammation (resulting from an inadequate immune response) is probably the main cause of ALA. Reports referring to inflammatory mechanisms of liver damage mention a repertoire of toxic molecules by the immune response (especially nitric oxide and reactive oxygen intermediates) and cytotoxic substances released by neutrophils and macrophages after being lysed by amoebas (e.g., defensins, complement, and proteases). Nevertheless, recent evidence downplays these mechanisms in abscess formation and emphasizes the importance of peroxynitrite (ONOO−). It seems that the defense mechanism of amoebas against ONOO−, namely, the amebic thioredoxin system (including peroxiredoxin), is superior to that of mammals. The aim of the present text is to define the importance of ONOO− as the main agent of liver abscess formation during amebic invasion, and to explain the superior capacity of amoebas to defend themselves against this toxic agent through the peroxiredoxin and thioredoxin system.

Invasive amebiasis: A microcirculatory disorder?

The two current models of invasive amebiasis both hold that direct contact of toxic molecules and amebas with tissue produces the necrotic areas characteristic of this disorder. Whereas one model characterizes these toxic molecules as amebic products (e.g., lectins, amebapores, cysteine proteinases and other proteolytic enzymes), the other describes them as products of the inflammatory response (e.g., cytokines, nitric oxide, reactive oxygen intermediates and cytotoxic granules). Both these models can account for necrotic areas with many amebas present and with acute inflammation, but not those with few or no amebas present or with scarce inflammation. A new model poses that an inadequate immune response leads to a continuous and prolonged activation of endothelial cells (ECs) by amebas, amebic molecules and cytokines, which triggers the mechanisms leading to necrosis. Other toxic molecules later contribute to EC activation: nitric oxide, reactive oxygen intermediates, the activated complement and proteases. Hyperactivated endothelial cells continuously express adhesion molecules (e.g., ICAM-1 and E-selectin), pro-coagulant molecules (e.g., tissue factor, von Willebrand factor, and the plasminogen activator inhibitor), resulting in ever greater inflammation and thrombosis, which eventually reduces or blocks blood flow in some vessels and starves certain tissue areas of an adequate oxygen and nutrient supply. When necrotic areas first develop, they are surrounded by inflammatory cells due to the acute inflammation at this stage. However, these cells are starved of oxygen and essential nutrients by the same microcirculatory dysfunction. The increasing concentration of nitric oxide during amebiasis eventually has an anti-inflammatory and vasodilating effect, creating a new mechanism for the microcirculatory dysfunction. This local microcirculatory dysfunction can explain necrotic areas in the presence of many, few, or no amebas, with abundant or scarce inflammation.

Nasal IgA secretion in a murine model of acute stress. The possible role of catecholamines.

Stress stimuli affect the immune system of the mucosa, and in particular IgA secretion. It is well documented that intense psychological and physical stress can increase susceptibility to infection by diverse pathogens in the upper respiratory tract. Our workgroup reported that chronic stress caused by immobilization elicits a decrease in nasal IgA levels in mice. Here, we explore how acute stress (caused by 4h of immobilization) affects IgA secretion in the nasal mucosa, and the possible role of the sympathetic nervous system in this effect. Nine-week-old male CD1 mice were divided into four groups: control, chemical sympathectomy (with 6-OHDA) and treatment with nadolol (5mg/kg) or phentolamine (15mg/kg). All these groups were subdivided into stressed and unstressed animals. The parameters evaluated included plasma corticosterone and epinephrine (only in control groups), SIgA levels (by ELISA) and SIgA expression (by Western Blot) in nasal fluid, percentage of IgA+ plasma cells, and mRNA expression of heavy alpha chain, pIgR, TNFα and TGFβ in nasal mucosa. Acute stress reduced the percentage of IgA+ cells while increasing the levels of IgA, the two hormones, and the mRNA expression of heavy alpha chain, pIgR, TNFα and TGFβ, which resulted in greater synthesis and transport of IgA. The treatments with 6-OHDA and α- and β-adrenergic receptor blockers suggest that sympathetic innervation by both types of adrenergic receptors is important for the control of SIgA secretion in nasal mucosa during acute stress. The increase in this parameter depended on the cytokines involved in IgA synthesis and transport.

Role of the striatum in the humoral immune response to thymus-independent and thymus-dependent antigens in rats

Since the role of striatal GABAergic medium-sized spiny (MSP) neurons in the modulation of the immune responses is largely unknown, we evaluated the humoral immune response in rats with bilateral lesion of the striatum caused by quinolinic acid, which destroys MSP neurons. Sham-operated rats and those with striatal lesions were immunized either with TNP-LPS, a T-independent antigen type 1, or one of several T-dependent antigens: ovoalbumin, bovine serum albumin, lysozyme, sheep red blood cells (SRBC) or outer membrane proteins (OMP) of Salmonella enterica serovar Typhimurium. The specific levels of serum IgM and IgG, as well as intestinal IgA antibodies were determined either by enzyme-linked immunosorbent assay (ELISA) or a haemagglutination assay 5 or 7 days after immunization. Our results show that the lesion of striatal MSP neurons attenuated the primary antibody response to the T-independent antigen type 1 (TNP-LPS), but increased the antibody response to T-dependent antigens (proteins, SRBC and OMP), indicating that the striatal neurons modulate the humoral immune response in rats. The mechanisms involved are probably related to a reduction in both the number of B cells and the expression of caveolin-1 in the spleen, as well as an increase in the number of CD4(+) T cells and in corticosterone levels of the serum.

Effect of Diet and Exercise on the Peripheral Immune System in Young Balb/c Mice

Although diet and exercise clearly have an influence on immune function, studies are scarce on the effect caused by exercise and the consumption of a carbohydrate-rich or fat-rich diet on the peripheral immune system. The aim of the present study was to evaluate the effect of exercise and the two aforementioned unbalanced diets on young Balb/c mice, especially in relation to BMI, the level of glucose, and the percentage of lymphocyte subpopulations in peripheral blood. The changes found were then related to the synthesis of leptin and adiponectin as well as the production of oxidative stress. The increase in BMI found with the carbohydrate-rich and fat-rich diets showed correlation with the levels of leptin and adiponectin. An increase in leptin and a decrease in adiponectin directly correlated with an increase in total lymphocytes and CD4+ cells and with a decrease in B cells. The increase in leptin also correlated with an increase in CD8+ cells. Glycemia and oxidative stress increased with the two unbalanced diets, negatively affecting the proliferation of total lymphocytes and the percentage of B cells, apparently by causing alterations in proteins through carbonylation. These alterations caused by an unbalanced diet were not modified by moderate exercise.

Intermittent fasting promotes bacterial clearance and intestinal IgA production in Salmonella typhimurium-infected mice.

The impact of intermittent fasting versus ad libitum feeding during Salmonella typhimurium infection was evaluated in terms of duodenum IgA levels, bacterial clearance and intestinal and extra‐intestinal infection susceptibility. Mice that were intermittently fasted for 12 weeks or fed ad libitum were infected with S. typhimurium and assessed at 7 and 14 days post‐infection. Next, we evaluated bacterial load in the faeces, Peyers patches, spleen and liver by plate counting, as well as total and specific intestinal IgA and plasmatic corticosterone levels (by immunoenzymatic assay) and lamina propria IgA levels in plasma cells (by cytofluorometry). Polymeric immunoglobulin receptor, α‐ and J‐chains, Pax‐5 factor, pro‐inflammatory cytokine (tumour necrosis factor‐α and interferon‐γ) and anti‐inflammatory cytokine (transforming growth factor‐β) mRNA levels were assessed in mucosal and liver samples (by real‐time PCR). Compared with the infected ad libitum mice, the intermittently fasted infected animals had (1) lower intestinal and systemic bacterial loads; (2) higher SIgA and IgA plasma cell levels; (3) higher mRNA expression of most intestinal parameters; and (4) increased or decreased corticosterone levels on day 7 and 14 post‐infection, respectively. No contribution of liver IgA was observed at the intestinal level. Apparently, the changes following metabolic stress induced by intermittent fasting during food deprivation days increased the resistance to S. typhimurium infection by triggering intestinal IgA production and presumably, pathogen elimination by phagocytic inflammatory cells.