**6. Conclusion**

expression is constitutive [60]. However in mammals, hepatic CRP is soluble in nature which is released into circulation [62] induced by proinflammatory cytokines. Recently, in an interest‐ ing study, the evolutionary significance of TNF, IFNγ and iNOS in immune response has been amply demonstrated in two Indian mollusc species [63]. Besides assessing different toxicologi‐ cal parameters, anti‐bacterial property of the innate immune molecule, namely C‐reactive pro‐ tein (CRP) isolated from *A. fulica*, was also determined. CRP is a prototypic acute phase reactant, which is a phylogenetically conserved protein expressed in invertebrates such as arthropods [56], molluscs [58] and also in all vertebrates [64]. In *Limulus*, an arthropod, CRP acts as a main front‐line innate immune molecule [59] which may be the key to a powerful defense mecha‐ nism of these animals against microbial infections that are potentially lethal in other organisms. Moreover, the presence of high level of endogenous CRP (2–4 mg/ml) in the hemolymph of *A.* 

*fulica* [58] might be the sole reason behind their effective survival in the environment.

Several authors reported that CRP can protect mice from infections caused by both Gram‐posi‐ tive *Streptococcus pneumoniae* [65] and Gram‐negative *Neisseria elactamica* [66] and *Haemophilus influenzae* [67] bacteria via direct binding with repetitive phosphorylcholine moieties on the lipo‐ teichoic acid or the lipopolysaccharide (LPS) of these pathogens, respectively. The level of CRP also increases dramatically during periods of immunological challenge and boosts the bacteri‐ cidal activities of monocytes and neutrophils by enhancing the release of reactive oxygen inter‐ mediates [68]. CRP also induces oxidative stress in vitro in endothelial cells, smooth muscle cells and monocyte‐macrophages [69, 70]. Although there are many reports on properties of CRP in a wide range of in vitro and in vivo model systems, clear understanding of the actual biological functions of this phylogenetically ancient and highly conserved molecule remains elusive.

It is also noted that bacterial cells are strongly dependent on metabolic cycles for their sur‐ vival and pathogenicity [71, 72]. Therefore, effect of *Achatina* CRP (ACRP) on these bacterial metabolic cycles comprising key metabolic enzymes such as phosphofructokinase 1(PFK1) in glycolysis, isocitrate dehydrogenase (ICDH) and isocitrate lyase (IL) in TCA cycle and fruc‐ tose‐1,6‐bis phosphatase (FBP1) in gluconeogenesis was also investigated. Various authors have reported the existence of eukaryote‐like programmed cell death and the involvement of caspase‐3‐like proteins in bacteria [73]. Based on this information, it was attempted to delin‐ eate the anti‐bacterial property of ACRP in terms of inhibition of salient metabolic enzymes which decrease bacterial infection accompanied by ROS generation and apoptosis‐like phe‐

Several authors [74] reported potentiality of human CRP to inhibit superoxide (O2

tion and delay apoptosis in neutrophils [64]. Recently, it has been reported that immune‐ potent CRP modulates antioxidant and anti‐inflammatory effects in LPS‐stimulated human macrophages [75]. The anti‐stress property of ACRP was tested in mice which are known to have a very low level of endogenous CRP (∼2 μg/mL) even after an inflammatory stimulus [76]. In order to prove this hypothesis, lead nitrate was administered intraperitoneally at an environmentally relevant dose in mice, and the induced oxidative stress was found to be removed when ACRP was administered prior to treating with Pb*.* Furthermore, in an in vitro study, both native CRP and its subunits were found to accomplish reversal of lead‐induced

−

) genera‐

notypes during bacterial cell death.

224 Organismal and Molecular Malacology

hepatotoxicity in *A. fulica* [77].

Presently immunological molecules in mollusc, especially *A. fulica* have gained much atten‐ tion because they fail to synthesize immunoglobulins but possess a strong innate immune sys‐ tem comprised of several molecules such as microbial surface antigens lipopolysaccharides (LPS)/endotoxins, glucans, acharan sulfate‐glycosaminoglycan, achacin‐mucus–derived anti‐ bacterial protein, hemocyte‐derived factors and C‐reactive protein. Among these proteins, CRP not only acts as apotent defence molecule but also engages in several vital physiological functions. Recently, elegant studies have clearly indicated the role of *Achatina* CRP in inhibit‐ ing growth of both Gram‐positive and Gram‐negative human pathogenic bacteria [88]. These investigations showed for the first time that CRP itself can trigger apoptotic like cell death in bacterial cells. Another important contribution from this group is that ACRP was found to cross species barrier and reduce metal toxicity in mammals (mice). However, more in depth study is warranted to exploit these molecules for the benefit of human beings.
