Fishes are the most successful and diverse group of vertebrate animals, first appeared during Devonian period. Despite of certain differences, the immune system of fish is physiologically similar to that of higher vertebrates. The heterogenous group of fishes are the apparent link between innate immunity and the first appearance of the adaptive immune response. Importantly, fishes have immune organs homologous to that of mammalian immune system. In comparison to higher vertebrates, fishes live free in their environment from the early embryonic stage and during that time mostly they are dependent on non-specific immune system for their survival. In the fishes, non-specific immunity is the fundamental defense mechanism, therewith acquired immunity also plays key role in maintaining homeostasis by activation though a system of receptors proteins, which identify pathogen associated molecular pattern typical of pathogenic microorganism includes lipopolysaccharides, peptidoglycans, DNA, RNA and other molecules that are typically not present on the surface of multicellular organism. There are several external factors like environmental factors, biological factors, stress and internal factors like genetic makeup, age and sex, maternal effect etc. can affect immunological defense capabilities of the fishes.

Stromelysin-3(MMP-11) is a matrix-metalloproteinase known to be over expressed in invasive tumors of human origin and suppose to have a potential role in metastasis. Dog mammary tumors are usually very invasive. Thus to characterize dog stromelysin-3, mammary tumor tissue (papillary adenocarcinoma) was used to isolate the protein by using affinity chromatography tools including Cibacron-Blue 3GA-CL Agarose, gelatin Sepharose, and heparin Sepharose columns. Western blotting with antihuman stromelysin-3 antibody was done for identification. The result showed a heavier (120kDa) protein than the expected size of stromelysin-3. Western blot analysis of the crude sample did not show any other reactive bands. Under reducing condition, the protein size remained intact. The stromelysin-3 like protein showed mild caseinolytic activity, which increased by activators like APMA and trypsin. Whereas, its activity decreased when inhibitors like EDTA, 1, 10-Phenanthroline and TIMP-1 were used suggesting the requirement of calcium and zinc for enzyme activity just like any other metalloproteinase.