Cell migration induced by Leishmania (Leishmania) amazonensis, Leishmania (Leishmania) major and Leishmania (Viannia) braziliensis into the peritoneal cavity of BALB/c mice

SHORT COMMUNICATION

Cell migration induced by Leishmania (Leishmania) amazonensis, Leishmania (Leishmania) major and Leishmania (Viannia) braziliensis into the peritoneal cavity of BALB/c mice

Wakimoto DT^I; Gaspareto KV^I; Silveira TGV^II; Lonardoni MVC^II; Aristides SMA^II

^IGraduate Program, State University of Maringá, Maringá, Paraná State, Brazil

^IIDepartment of Clinical Analysis, State University of Maringá, Maringá, Paraná State, Brazil

^{Correspondence to}

ABSTRACT

In American cutaneous leishmaniasis, the initial infection phase is characterized by recruitment of neutrophils and monocytes. The migration of these cells in response to the presence of Leishmania in the peritoneum of affected animals remains unclear. The objective of this study was to investigate cell migration to the peritoneum of BALB/c mice after infection with Leishmania (Leishmania) amazonensis, Leishmania (Viannia) braziliensis and Leishmania (Leishmania) major. Initially, Leishmania spp. was intraperitoneally inoculated in five groups of six animals each and the cell migration was analyzed 0, 3, 6, 12, 24 and 48 hours after infection. Different cell counts were performed with a staining kit and showed a higher percentage of polymorphonuclear than mononuclear cells in all three species studied. The total cell count revealed peak migration in L. (L.) amazonensis and L. (L.) major at six hours, and in L. (V.) braziliensis at 12 hours. These results suggest that factors released from different cell types probably act by attracting polymorphonuclear cells, with the peak migration most likely depending on the species of Leishmania inoculated into the host.

Key words: BALB/c mice, Leishmania spp., American cutaneous leishmaniasis.

INTRODUCTION

In the initial phase of infection, American cutaneous leishmaniasis (ACL) lesions are characterized by the recruitment of blood neutrophils and monocytes (1). Leucoytes play an important role in host defense, and their recruitment to infected tissue may constitute a crucial event in the control of infections such as leishmaniasis. Peters et al. (2) reported that neutrophilis are rapidly mobilized to sandfly bite sites, where they phagocytose L. major parasites. While the saliva of the transmitter insect increases mouse macrophage chemotaxis, lipophosphoglycan (LPG) - the main component of the surface of Leishmania - reduces it, highlighting the capacity of this molecule to damage phagocyte responses (3-5). Chen et al. (6) reported that neutrophils may play an important role in the development of resistance to T. cruzi infection in BALB/c mice, despite the fact that neutrophil depletion reduces the degree of infection by T. cruzi in C57BL/6 mice, possibly through modulating the Th1/Th2 dichotomy in different directions. Other studies have shown that neutrophils may contribute to the immunopathology in experimental cerebral malaria (7, 8). These examples show the paradox and complexity of the roles of neutrophils in infections.

It is well known that the polymorphonuclear cells (PMN) are the first line of defense against infections and have a prolonged lifespan of approximately 6 to 10 hours in the bloodstream, after which they undergo spontaneous apoptosis (9). According to Aga et al. (10), these cells have their survival time increased by the inhibition of apoptosis induced by Leishmania parasite, predisposing them to serve as hosts to the parasites in the initial phase of infection. Lima et al. (11) have already reported that neutrophils present a leishmanicidal activity by holding back the spread of the parasite at the beginning of the infection. However, the precise immunoregulatory role of PMN infected with Leishmania is not completely understood. Previous findings document in vitro migration; however, in in vivo migration, in an air pouch model, the injection of L. major and L. donovani led to a rapid and transient accumulation of leucocytes (12). Although it seems ideal to use polymorphornuclear and mononuclear infiltrates in the injured skin to examine the function of these cells, it is almost impossible to obtain enough cells from local tissues for this purpose (13). Thus, we proposed the use of in vivo migration of these cells in response to Leishmania spp. in the mouse peritoneum.

The aim of this study was, therefore, to study the in vivo migration of polymorphonuclear and monocyte cells to the peritoneum of BALB/c mice in response to infection by L. (L.) amazonensis, L. (V.) braziliensis and L. (L.) major.

The procedures followed the regulations established by the Brazilian College of Animal Experimentation (COBEA) and the study was approved by the Ethics Committee for Animal Experimentation of the State University of Maringá. The results were analyzed by a non-parametric ANOVA using the Bonferroni test for multiple comparisons and t-tests, with Welch correction, for dual comparisons. A "p" value below 0.05 was considered significant.

In the current study, stationary-phase promastigotes (2 x 10⁶ parasites in 0.1 mL of PBS) of L. (L.) amazonensis (MHOM/BR/1989/166MJO), L. (V.) braziliensis (MHOM/BR/1987/M11272) and L. (L.) major (LV39) were intraperitoneally inoculated in six BALB/c mice (7 to 12 weeks old) per experimental group. At different moments after the inoculation [0 (control), 3, 6, 12, 24 and 48 hours], the animals were lethally anesthetized [80 mg/kg of ketamine plus 16 mg/kg of xylazine (14)], and the peritoneal contents were washed with a total of 5 mL of Hank's solution to collect leukocytes from the exudates. The only two experiments were performed on different days.

The mean viability of the cells obtained from the peritoneal exudates at the different times, verified by trypan blue exclusion (0.1%), was found to be 96%. Cellular differentiation between polymorphonuclear and mononuclear cells was performed microscopically in the smears on a plate stained with a Panotico® kit (Laborclin, Brazil). The percentage of polymorphonuclear cells that migrated to the peritoneum was greater than that of the mononuclears for the different Leishmania species. L. (L.) major was not statistically different from the control group after 3, 6 and 24 hours of infection. Statistical difference was observed in L. (L.) amazonensis at the times of 6, 12 and 24 hours, whereas L. (V.) braziliensis differed statistically after 12 hours of infection in relation to controls. However, there was no significant difference among the three species of Leishmania evaluated (Table 1).

Recruited cells were counted directly with Turk's solution in a Neubauer chamber. The peaks in cell migration into the peritoneal cavity were observed at six hours in mice inoculed with L. (L.) amazonensis and L. (L.) major, and at 12 hours in those inoculed with L. (V.) braziliensis. When the time periods of 3, 6, 12, 24 and 48 hours were compared among the three Leishmania species, no statistically significant differences were found. When the controls (0 hour) were compared with the different time periods for L. (L.) amazonensis, statistical differences were observed at six hours (39 x 10⁶ cells/mL), 12 hours (11 x 10⁶ cells/mL) and 24 hours (14 x 10⁶ cells/mL); L. (V.) braziliensis differed statistically at 12 hours (18 x 10⁶ cells/mL), whereas L. (L.) major presented differences at three hours (12 x 10⁶ cells/mL), six hours (12 x 10⁶ cells/mL) and 24 hours (5.4 x 10⁶ cells/mL) (Table 2).

In the current study, the presence of a greater number of PMN, compared to mononuclears, at the beginning of the infection agrees with the results obtained in vitro using a chemotactic assay of human leucocytes (15). Furthermore, in agreement with the findings from the in vivo air pouch model obtained by Matte and Olivier (12), from the paw inoculation of animals and draining lymph nodes, it was reported herein that the PMN had been found in large numbers in infiltrates at the lesion sites after inoculation with L. (L.) major in BALB/c mice (11, 16).

The migration peaks may be related to the release of inflammatory factors at the infection site, and direct the type of immune response from the host, while the cellular diversity and accumulation may be associated with the expression pattern of the chemokine genes (12). Similarly, Romani et al. (17) reported that the production of IL-10 or IL-12 by neutrophils in mice with candidiasis is associated with development of a Th1 or Th2 response, respectively. The immune response to leishmaniasis can result in a polarization of a subpopulation of T lymphocytes, which leads to a different cell phenotype and results in immune protection or exacerbation of the disease (18). Furthermore, Tacchini-Cottier et al. (19) reported that the influx of neutrophils in the first 24 hours modifies the response of T cells, via production of IL-4, and the susceptibility to infection by L. major, by developing a Th2 response. In addition, van Zandbergen et al. (15) demonstrated that Leishmania promastigotes induce the migration of PMN by releasing Leishmania chemotactic factor (LCF), and that the co-incubation of Leishmania with PMN inhibits the CXC chemokine interferon gamma-inducible protein 10 (IP-10), suggesting that Leishmania inhibits the activity of Th1 or NK cells and, consequently, interferes with the development of the protective immune response.

Matte and Olivier (12) reported that the inflammatory events of leishmaniasis that occur at the inoculation site could direct the type of species-specific pathogenesis that will be developed subsequently. Tacchini-Cottier et al. (19) suggested that the initial accumulation and persistence of PMN could be linked to the possible immunoregulatory role of these cells, or even better, to the development of the Th2 response that is characteristic of mice susceptible to L. major. Furthermore, in resistant mice (C57BL/6), the percentage of neutrophils infected with L. major fell from 60% to less than 10%, 72 hours after infection, by predisposing the mice to the development of the Th1 response. In the present study the peak at six hours coincided with that obtained by Matte and Olivier (12) in the air pouch model, after inoculation with L. (L.) major. It was deduced that the longer PMN peak (at six hours) in BALB/c mice susceptible to L. (L.) major and L. (L.) amazonensis corresponds to the shorter Leishmania retention time presented by the polymorphonuclear cells. Conversely, in this mouse lineage, which is resistant to L. (V.) braziliensis, the 12-hour peak corresponds to the longer Leishmania retention time displayed by the PMN.

In conclusion, compared with other studies, these results suggest that factors released by different cell types act by attracting cells, mainly polymorphonuclears, to the peritoneal exudate of BALB/c mice in the initial phase of infection, predisposing the animals to either susceptibility or resistence to the infection. The migration of a large number of cells to the infection site - which occurs at six hours for L. (L.) amazonensis and L. (L.) major and at 12 hours for L. (V.) braziliensis - suggests that the release of these factors is greater at these times and depends on the species of the parasite involved and on the immune response of the host.

Received: October 6, 2009

Accepted: October 27, 2009

Abstract published online: November 16, 2009

Full paper published online: February 28, 2010

Conflicts of interest: There is no conflict.

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Publication Dates

• Publication in this collection
  18 Mar 2010
• Date of issue
  2010

History

• Received
  06 Oct 2009
• Accepted
  02 Nov 2009