Abstract
Mycoplasmas are a large group of prokaryotes which is believed to be originated from Gram-positive bacteria via degenerative evolution, and mainly capable of causing a wide range of human and animal infections. Although innate immunity and adaptive immunity play crucial roles in preventing mycoplasma infection, immune response that develops after infection fails to completely eliminate this bacterium under certain circumstances. Thus, it is reasonable to speculate that mycoplasmas employ some mechanisms to deal with coercion of host defense system. In this review, we will highlight and provide a comprehensive overview of immune evasion strategies that have emerged in mycoplasma infection, which can be divided into four aspects: (i) Molecular mimicry and antigenic variation on the surface of the bacteria to evade the immune surveillance; (ii) Overcoming the immune effector molecules assaults: Induction of detoxified enzymes to degradation of reactive oxygen species; Expression of nucleases to degrade the neutrophil extracellular traps to avoid killing by Neutrophil; Capture and cleavage of immunoglobulins to evade humoral immune response; (iii) Persistent survival: Invading into the host cell to escape the immune damage; Formation of a biofilm to establish a persistent infection; (iv) Modulation of the immune system to down-regulate the intensity of immune response. All of these features increase the probability of mycoplasma survival in the host and lead to a persistent, chronic infections. A profound understanding on the mycoplasma to subvert the immune system will help us to better understand why mycoplasma is so difficult to eradicate and ultimately provide new insights on the development of therapeutic regimens against this bacterium in future.
Highlights
Mycoplasmas are the smallest and simplest self-replicating organisms
The basic structure is simpler than the common Gram-negative bacteria, there is a complex cross-talk between mycoplasma and the host immune system involving mycoplasma-induced non-specific and specific immune responses
The most frequently discussed examples related to molecular mimicry is the Guillain–Barré syndrome, which is induced by M. pneumoniae infection with a lipid structure that results in the enhancement of galactocerebrosidespecific antibodies level from patients
Summary
Mycoplasmas (class Mollicutes) are the smallest and simplest self-replicating organisms. The most frequently discussed examples related to molecular mimicry is the Guillain–Barré syndrome, which is induced by M. pneumoniae infection with a lipid structure that results in the enhancement of galactocerebrosidespecific antibodies level from patients This cross-reactivity is relevant for autoimmunity and might be exploited by mycoplasmas to avoid recognition by the adaptive immune system (Kusunoki et al, 2001). The authors found that one or more of these mechanisms could concomitantly result in diverse antigenic variation and be implicated in many relevant gene families, including the mpl, mgp, lmp, mba, vip, vihA, vmc, vsa, vsp, and vpma gene families These gene families have never been reported to exist in some of the important pathogenic mycoplasma species, such as M. pneumoniae and M. fermentans. Ohr: MG454, MPN668 OsmC: MG427, MPN625 MsrA: MPN662, MG408 Other: Ferritin-like protein
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