Molecular Aspects of Neutrophils as Pivotal Circulating Cellular Innate Immune Systems to Protect Mammary Gland from Pathogens

Abstract

As a pivotally cellular and molecular arms of circulating innate immune system, polymorphonuclear cells (PMNs) are the most vital primary mobile phagocytes in the body of mammals; their appropriate function is very essential to enhance animals’ and humans’ health performance. As the first type of innate immune cells arriving at the site of infection, neutrophils play a key role in initiating an innate, inflammatory, and specific immune responses; their importance for protection of organs in the body from pathogens has long been a crucial concern (Burvenich et al., 1994; Paape et al., 1996; Reeves et al., 2002; Burvenich et al., 2003; Mehrzad et al., 2004; 2005a; Letiember, et al., 2005; Liu et al., 2005; Borregaard et al., 2007; Stevens, et al., 2011a; 2011b; Bruhn et al., 2011). The proof of vital roles of neutrophils is that the neutropenic animals/humans are always highly susceptible to many pathogens. Clearly, the complex phenomenon of PMN chemotaxis, diapedesis, phagocytosis, and eventually microbicidal activity each contributes to the ability of PMN to provide an effective first line defense for the body and organs like udder (Burvenich et al., 2003; Mehrzad et al., 2000; 2001a; 2001b; 2002a; 2002b; 2004; 2005a; 2007; 2008a; 2008b; 2009; Mayadas & Cullere, 2005; Borregaard et al., 2008). In this concept many powerful afferent (sensing) and efferent (effector) arms of the neutrophils inside and outside of the cytoplasm are involved; the most common arms are enzymes, granules, free radicals or reactive oxygen species (ROS) and reactive nitrogen species (RNS) and in phagolysosome, into which microbicidal agents are released, neutrophil extracellular traps (NETs), neutrophils’ membrane receptors like pattern recognition receptors (PRRs), opsonin receptors etc. that sense, bind and efficiently kill invading microbes, destroy virulence factors, or prevent them from spreading.