Highly purified lipoteichoic acid activates neutrophil granulocytes and delays their spontaneous apoptosis via CD14 and TLR2

Abstract

Lipoteichoic acid (LTA) is a major component of the cell membrane of gram-positive bacteria. Although LTA has become increasingly recognized as an immunomodulator, its effect on polymorphonuclear neutrophil granulocytes (PMN) is still not clear. The interaction between LTA and PMN, however, is of particular importance, as PMN are the first leukocytes that migrate to the site of infection and encounter bacterial pathogens. In the present study, the interaction of highly purified human PMN with endotoxin-free LTA from Staphylococcus aureus was investigated. After exposure to LTA, neutrophil granulocytes acquired typical activated cell morphology. LTA had a marked activating effect on the functions of PMN as well. Shedding of CD62L, degranulation, and priming for formyl-Met-Leu-Phe-mediated oxidative burst were induced in PMN upon exposure to LTA. Moreover, LTA treatment induced the release of proinflammatory cytokines such as interleukin-8, tumor necrosis factor alpha, and granulocyte-colony stimulating factor by PMN. The effects of LTA on PMN were found to be associated with nuclear factor-kappaB activation. Of particular interest was that LTA inhibited the spontaneous apoptosis and therefore, increased the lifespan of PMN. Experiments using blocking antibodies revealed that CD14 and Toll-like receptor 2 (TLR2) but not TLR4 play a major role in LTA-mediated effects on PMN. These data clearly show that LTA, a component of gram-positive bacteria, directly activates neutrophil granulocytes, the primary effector cells in the first line of defense against infectious challenge.

Recombinant human Hsp70 protects against lipoteichoic acid-induced inflammation manifestations at the cellular and organismal levels

“…6). This value coincides with the results of other authors (Lotz et al 2004). In these series of experiments, apoptosis of neutrophils not treated with LTA was considered to be 100%.…”

“…On the other hand, LPS administration resulted in approximately the same ROS concentration increase when much lower concentrations of the toxin were applied (1-20 ng/ml; Lotz et al 2004;Rozhkova et al 2010). It is noteworthy that although the delivery of both toxins (LTA and LPS) occurs via CD14 receptors (Lotz et al 2004;Leon et al 2008), only about 7,000 receptors can be activated in neutrophils, while in monocytes, more than 100,000 of these receptors can be expressed (Antal-Szalmas 2000). Furthermore, both LTA and LPS administration to myeloid cells results in the enhanced expression of CD11b/CD18 adhesion receptors (Carratelli et al 1996), as well as enhanced LPS activity (Detmers et al 1998).…”

“…TLR4 and TLR2, in cooperation with the CD14 receptor, recognize Gram-negative or Gram-positive pathogens, respectively. Lipoteichoic acid, which represents the major component of the Gram-positive bacterial cell wall, stimulates mammalian phagocytes by activating the TLR2, CD14, and CD36 receptors (Lotz et al 2004;Nilsen et al 2008). LPS activates phagocytes that explore components of the TLR4/CD14/MD2 complex as well as a few other proteins and receptors (Leon et al 2008).…”

“…Intracellular generation of reactive oxygen species (ROS) serves to maintain homeostasis; therefore, ROS production is strictly controlled. Both LPS and LTA strongly induce the level of ROS production, enhance the expression of CD11b/CD18 receptors, and inhibit neutrophils apoptosis (Lotz et al 2004;Detmers et al 1998). The development of systematic inflammation response syndrome and the subsequent manifestations of multiple organ dysfunction syndrome (MODS) result in the rapid progression of septic shock, which often leads to death (Bone 1991;Vincent 2008).…”

“…Thus, in Gram-positive bacteria, these components are represented by lipoteichoic acid (LTA; Fischer et al 1990;Lappin and Ferguson 2009); for Gram-negative flora, these components are lipopolysaccharide (LPS). In the early stages of bacterial infection, structural components of Gram-positive and Gram-negative bacteria interact with specific Toll-like receptors (TLRs) of macrophages, neutrophils, and monocytes (Leaver et al 2008;Lotz et al 2004;Detmers et al 1998).…”