Mirjana Dimitrijević

Can food-related environmental factors induce different behaviour in two key serovars, 4b and 1/2a, of Listeria monocytogenes?

Listeria monocytogenes isolates (81 in total; 42 isolated from cases of human listeriosis: 39 isolated from food), belonging to serovars 1/2a or 4b, were studied for any group differences between serovars to selected factors associated with foods (two bacteriocins and mild heat treatment), growth kinetics at 37 degrees C and pathogenicity for chick embryos. The isolates were tested for sensitivity to two bacteriocins at 4 degrees C and 37 degrees C, and were tested for the remaining parameters both before and after exposure to cold storage (4 degrees C) with starvation. In addition, the isolates were typed using pulsed field gel electrophoresis (PFGE), multilocus enzyme electrophoresis (MEE) and phage typing to find any correlation between the types and group differences in the chosen parameters. Considerable strain diversity within each L. monocytogenes serovar with respect to the chosen parameters was observed, especially after exposure to cold storage. Nevertheless, the serovar 1/2a isolates, as a group, tended to be more resistant to the two antilisterial bacteriocins at 4 degrees C than the group of serovar 4b isolates. In contrast, after cold storage at 4 degrees C, L. monocytogenes serovar 4b isolates, as a group, tended to be more resistant to heat treatment at 60 degrees C than the group of 1/2a isolates. In addition, the serovar 4b group tended to have shorter lag phases and higher pathogenicity, when transferred from cold storage to body temperature (37 degrees C), than the group of serovar 1/2a isolates. No correlation between PFGE-, MEE- and phage-types and the tested parameters was found. Although the above serovar-related differences were observed only when mean values of the groups were compared (not all isolates within each group followed the group pattern), the results indicate interesting directions for further research.

Effect of early experience on behavior and immune response in the rat

The effect of maternal deprivation (MD) and preweaning handling on open field (OF) behavior, body and organ weights (spleen, thymus, and adrenals), and humoral immune response (plaque-forming cell response and antibody production) in adult male and female Wistar rats was studied. Maternal deprivation took place either for 28 postnatal days (2 h/day), or on days 15, 18, and 21 (2 h/day), whereas handling was performed daily during 28 postnatal days for 3 min. Sex differences were found both in behavior and immune response. The MD rats showed ambulatory hyperactivity in OF tests, females being more active than males, and a marked suppression of the PFC response. Handled rats behavior was distinguishable from MD rats by an increased curiosity. Female handled rats were more active in the OF and their antibody production was higher. Male handled rats showed higher defecation scores and lower plaque-forming cell response. These results present evidence for a deprivation syndrome and immunosuppressive behavior in MD rats. Several mechanisms that may account for these immunobehavioral results are outlined.

Effect of neuropeptide Y on inflammatory paw edema in the rat: involvement of peripheral NPY Y1 and Y5 receptors and interaction with dipeptidyl-peptidase IV (CD26).

Several lines of evidence suggest that neuropeptide Y (NPY) may exert regulatory effects in local inflammatory responses. Here, we show that intraplantarly (i.pl.) applied NPY, peptide YY (PYY), and an NPY Y5 receptor-selective agonist dose-dependently potentiate concanavalin A (Con A)-induced paw edema in the rat. The NPY Y1 receptor antagonist BIBO 3304 abolishes the pro-inflammatory action of both NPY and PYY while the dipeptidyl-peptidase IV (CD26) inhibitor Ile-thiazolidide exerted synergistic and potentiating effects in vivo. Taken together, the present data reveal an NPY Y1/Y5 receptor interplay and an involvement of CD26 in the NPY-induced potentiation of paw edema in the rat.

Neuropeptide Y and its receptor subtypes specifically modulate rat peritoneal macrophage functions in vitro: counter regulation through Y1 and Y2/5 receptors.

It is well documented that neuropeptide Y (NPY) exerts a wide range of biological functions through at least five NPY Y receptor subtypes (Y1-Y5), but its immunological effects only recently came into focus. Using NPY family peptides and NPY-related receptor-specific peptides as well as Y1 and Y2 receptor antagonists, we have tested which NPY Y receptors are involved in NPY-induced modulation of rat peritoneal macrophage function in vitro. NPY and PYY increased oxidative burst in phorbol myristate acetate (PMA)-stimulated macrophages involving activation of protein kinase C (PKC), and decreased it in zymosan-stimulated cells resembling inhibition of signaling pathways subsequent to binding of zymosan particles for the iC3b fragment receptor on macrophages. The combined treatment with NPY and NPY Y receptor antagonists revealed that NPY-induced potentiation of oxidative burst in PMA-stimulated cells is mediated through Y1 and Y2 receptors, while NPY-induced suppression in zymosan-stimulated cells is mediated through Y2 receptors only. NPY-related peptides differently modulated macrophage function, confirming involvement of NPY Y2 receptor in both potentiation and suppression of oxidative burst in these cells. Additionally, it was shown that NPY Y5 receptor mediated suppression of oxidative burst in PMA- and zymosan-stimulated macrophages. Taken together, the present data reveal an NPY Y1 and Y2/Y5 receptor interaction in NPY-induced modulation of macrophage functions related to inflammation.

Experimental allergic encephalomyelitis in adult DA rats subjected to neonatal handling or gentling

The present study investigated the effect of daily handling and gentling between postnatal days 1 and 28 on experimental allergic encephalomyelitis (EAE) in 8-week old DA rats. Handling consisted of removing pups from the mother, and placing them in the novel cage for 15 min. The gentling procedure included handling accompanied by 3 min of dorsal tactile stimulation before returning the pups to the nest cage. Adult rats of both sexes handled in infancy showed increased susceptibility to EAE, as revealed by higher incidence of the disease, and more severe clinical signs. Anti-myelin basic protein (MBP) autoantibodies were increased in handled males, and decreased in handled females, compared to controls. Gentling induced aggravation of clinical signs and histopathological lesions of EAE in males, while in gentled females suppression was observed. These results indicated that both neonatal handling and gentling aggravated EAE induced in adult male rats. In female rats handling exacerbated, and gentling suppressed clinical EAE. The overall effect of neonatal manipulations was more pronounced in males. Furthermore, in mothers separated from their offspring due to handling and gentling, and immunized for EAE at day 28 postpartum, earlier appearance of clinical signs, and increased frequency of relapses compared to control dams was recorded.

Methionine-Enkephalin Stimulates Hydrogen Peroxide and Nitric Oxide Production in Rat Peritoneal Macrophages: Interaction of μ, δ and κ Opioid Receptors

Objective: Methionine-enkephalin (MET) modulates various functions of macrophages related to both immune and inflammatory reactions in a naloxone reversible manner, suggesting that opioid receptors are involved in the regulation of macrophage activity. Since an endogenous opioid ligand might interact with more than one type of opioid receptor, the receptor interaction determines its effect on a particular function. Methods: In the present study we have investigated the involvement of different opioid receptor types/subtypes in MET-induced modulation of H₂O₂ and NO production in macrophages. Thioglycollate-elicited or resident rat peritoneal macrophages were treated in vitro with MET and/or specific antagonists of δ_1,2, δ₁, δ₂, µ and ĸ opioid receptors. Results: MET increased H₂O₂production inphorbol myristate acetate-stimulated rat peritoneal macrophages mainly through δ₁ opioid receptor. MET also enhanced NOproduction in rat peritoneal macrophages stimulated with lipopolysaccharide through δ₁ and µ opioid receptors. The blockade of µ and ĸ receptor facilitated a potentiating effect of MET on H₂O₂ release, and blockade of ĸ receptor further raised the MET-induced increase of NO production in macrophages. Conclusion: It is concluded that both negative and positive functional interaction between δ, µ and ĸ opioid receptors regulate the influence of MET on H₂O₂ and NO production in rat peritoneal macrophages.

Stress-induced suppression of experimental allergic encephalomyelitis in the rat

Numerous experiments have demonstrated that physical stress can alter immunological parameters. However, little attention has been paid to the interrelationship between stress and autoimmune processes. The present study was designed to determine the influence of electric shock and sound stress on the development of experimental allergic encephalomyelitis (EAE). Ten-week-old male DA rats highly susceptible to EAE were used. Rats were subjected to the stress procedure during 19 days either before or after immunization with intradermal injection of 0.1 ml of an emulsion containing guinea pig spinal cord (20 mg/rat) in an equal volume of complete Freunds adjuvant (CFA). In addition, rats received subcutaneous injection of Bordetella pertussis in the dorsum of the same foot. Electric stress procedure consisted of 80 inescapable, unpredictable tail shocks (5 s, 1 mA) delivered at the same time each day. Sound stress procedure consisted of exposure of rats to a 90 dB fire alarm bell which rings 60 times for 5 s during one hour, at the same time of the day. Rats were observed daily for clinical signs of EAE and survived animals were sacrificed on day 20 after immunization. The brain and spinal cord sections were examined histologically for mononuclear cell infiltrates characteristics for EAE. The results clearly indicate that inescapable tail shocks suppressed the appearance and development of EAE when rats were subjected to stress procedure during 19 days after immunization, but not when rats were stressed during 19 day before the induction of EAE. On the other hand, in rats exposed to sound stress there was only delay in the onset of the disease.

The intriguing mission of neuropeptide Y in the immune system

For many years, the central nervous system and the immune system were considered two autonomous entities. However, extensive research in the field of neuroimmunomodulation during the past decades has demonstrated the presence of different neuropeptides and their respective receptors in the immune cells. More importantly, it has provided evidence for the direct effects of neuropeptides on the immune cell functions. Neuropeptide Y (NPY) is generally considered the most abundant peptide in the central and peripheral nervous system. However, it is also distinguished by exhibiting pleiotropic functions in many other physiological systems, including the immune system. NPY affects the functions of the cells of the adaptive and innate immunity. In this respect, NPY is known to modulate immune cell trafficking, T helper cell differentiation, cytokine secretion, natural killer cell activity, phagocytosis and the production of reactive oxygen species. The specific Y receptors have been found in immune cells, and their expression is amplified upon immune stimulation. Different Y receptor subtypes may mediate an opposite effect of NPY on the particular function, thus underlining its regulatory role. Since the immune cells are capable of producing NPY upon appropriate stimulation, this peptide can regulate immune cell functions in an autocrine/paracrine manner. NPY also has important implications in several immune-mediated disorders, which affirms the clear need for further investigation of its role in either the mechanisms of the disease development or its possible therapeutic capacity. This review summarises the key points of NPY’s mission throughout the immune system.

The anti-inflammatory effect of neuropeptide Y (NPY) in rats is dependent on dipeptidyl peptidase 4 (DP4) activity and age

Neuropeptide Y (NPY)-induced modulation of the immune and inflammatory responses is regulated by tissue-specific expression of different receptor subtypes (Y1-Y6) and the activity of the enzyme dipeptidyl peptidase 4 (DP4, CD26) which terminates the action of NPY on Y1 receptor subtype. The present study investigated the age-dependent effect of NPY on inflammatory paw edema and macrophage nitric oxide production in Dark Agouti rats exhibiting a high-plasma DP4 activity, as acknowledged earlier. The results showed that NPY suppressed paw edema in adult and aged, but not in young rats. Furthermore, plasma DP4 activity decreased, while macrophage DP4 activity, as well as macrophage CD26 expression increased with aging. The use of NPY-related peptides and Y receptor-specific antagonists revealed that anti-inflammatory effect of NPY is mediated via Y1 and Y5 receptors. NPY-induced suppression of paw edema in young rats following inhibition of DP4 additionally emphasized the role for Y1 receptor in the anti-inflammatory action of NPY. In contrast to the in vivo situation, NPY stimulated macrophage nitric oxide production in vitro only in young rats, and this effect was mediated via Y1 and Y2 receptors. It can be concluded that age-dependant modulation of inflammatory reactions by NPY is determined by plasma, but not macrophage DP4 activity at different ages.

Behavior and severity of adjuvant arthritis in four rat strains

Previous research has suggested that behavioral traits of the histocompatible Lewis and Fischer strains of rats could be related to the difference in their susceptibility to adjuvant arthritis (AA). In the present study, the predictive value of behavioral markers in susceptibility to AA was investigated in nonhistocompatible inbred DA, Lewis, Albino Oxford (AO), and outbred Wistar strain. Behavioral profiles (open filed test and forced swim test) were determined prior to immunization with a single intradermal injection of complete Freunds adjuvant. Animals were daily scored for clinical signs of AA. The occurrence of certain behaviors and clinical indices of AA was significantly associated with strain membership. Discriminant analysis identified strain-related behavioral and illness profiles with very few overlaps among the phenotypes. Discriminant classification significantly exceeded the proportion of cases, which could have been correctly classified on the basis of chance. Open field behavior, in particular, exploration and grooming, differentiated among AA-susceptible and AA-resistant strains. Multiple regression analysis indicated that severity of AA (maximum clinical sign) can be predicted by the latency time and grooming behavior in the open field independently of strain membership. No clear distinction between AA-susceptible and AA-resistant strains was found with respect to forced swim test immobility. It was concluded that (a) strain-related genetic predisposition is important for the expression of certain behavioral traits and for susceptibility to AA and (b) open field behaviors, particularly grooming and latency, predict susceptibility to AA across different rat strains.