Anaplasma phagocytophilumDelay of Neutrophil Apoptosis through the p38 Mitogen-Activated Protein Kinase Signal Pathway

Abstract

Human granulocytic anaplasmosis is caused by the obligate intracellular bacterium Anaplasma phagocytophilum. The bacterium avoids host innate defenses in part by infecting, surviving in, and propagating in neutrophils, as well as by inhibiting neutrophil apoptosis. However, the mechanisms of A. phagocytophilum survival in neutrophils and the inhibition of spontaneous apoptosis are not well understood. In this study, we demonstrated that antiapoptotic Mcl-1 protein (Bcl-2 family) expression is maintained and that inhibition of procaspase-3 processing occurs in A. phagocytophilum-infected human neutrophils. An evaluation of p38 mitogen-activated protein kinase (MAPK) showed evidence of increased phosphorylation with infection. Moreover, antagonism of p38 MAPK by the inhibitor SB203580 reversed apoptosis inhibition in live or heat-killed A. phagocytophilum-infected neutrophils. A role for the autocrine or paracrine production of antiapoptotic interleukin 8 (IL-8) expressed with A. phagocytophilum infection was excluded by the use of IL-8-, IL-8R1 (CXCR1)-, and IL-8R2 (CXCR2)-blocking antibodies. As previously demonstrated, the antiapoptotic effect was initially mediated by exposure to A. phagocytophilum components in heat-killed bacteria. However, an important role for active infection is demonstrated by the additional delay in apoptosis with intracellular growth and the refractory abrogation of this response by the p38 MAPK inhibitor 3 to 6 h after neutrophil infection. These results suggest that the initial activation of the p38 MAPK pathway leading to A. phagocytophilum-delayed neutrophil apoptosis is bypassed with active intracellular infection. Moreover, active intracellular infection contributes more to the overall delay in apoptosis than do components of heat-killed A. phagocytophilum alone.

Delayed Human Neutrophil Apoptosis by Trichomonas vaginalis Lysate

“…These results suggest that the intrinsic mitochondrial pathway, including Mcl-1 and caspase-3, is involved in the delay of neutrophil apoptosis induced by T. vaginalis lysate. These results also correspond with the results of other studies which reported that Anaplasma phagocytophilum delayed neutrophil apoptosis via Mcl-1 and caspase-3 mechanisms [9]. Taken together, our results indicate that lysate of the human trichomonad, T. vaginalis, delayed human neutrophil apoptosis through inhibition of typical features of apoptosis such as decreased MMP, caspase-3 activation, and reduction of Mcl-1.…”

“…For example, trichomonads caused neutrophils to produce low levels of IL-8 compared to live T. vaginalis, and IL-8 may contribute to apoptotic changes of neutrophils [5]. IL-8 secretion was also observed with bacterial supernatant or Anaplasma phagocytophilum treated neutrophils, and apoptosis delay was also shown in these neutrophils [9,21]. Accordingly, it is suggested that a balance of viable trophozoites, lysates, and ESP form T. vaginalis may contribute to progression of inflammatory reactions in trichomoniasis via the control of neutrophil apoptosis.…”

“…This is necessary to avoid unwanted tissue damage caused by activated neutrophils around the infection site [7,9]. It is known that delayed neutrophil apoptosis is associated with the pathogenesis of several diseases such as rheumatoid arthritis and Crohn's disease [10,11].…”

Infection with Anaplasma phagocytophilum Activates the Phosphatidylinositol 3-Kinase/Akt and NF-κB Survival Pathways in Neutrophil Granulocytes

“…A. phagocytophilum replicates in the parasitophorous vacuole of neutrophil granulocytes and forms microcolonies called morulae. Previous reports show that infection with A. phagocytophilum delays neutrophil apoptosis by upregulating the p38 mitogen-activated protein kinase (MAPK) pathway (10) and by modulating extrinsic and intrinsic pathways of apoptosis (21). The phosphatidylinositol 3-kinase (PI3K)/Akt and NF-B pathways are considered as important survival signaling pathways in neutrophils (54).…”

“…In the circulation, neutrophils have a short life span: they undergo spontaneous apoptosis within 6 to 10 h. However, neutrophil apoptosis is delayed after exposure to proinflammatory stimuli such as interleukin-8 (IL-8), tumor necrosis factor alpha (TNF-␣), IL-1, IL-2, gamma interferon (IFN-␥), granulocyte-macrophage colony-stimulating factor (GM-CSF), G-CSF, or lipopolysaccharide (LPS) (3,25,28,39). In addition, several intracellular pathogens such as Anaplasma phagocytophilum, Leishmania major, Chlamydia pneumoniae, and respiratory syncytial virus have developed strategies to manipulate the spontaneous apoptosis of host neutrophils (1,10,47).…”