The beta defensins are antimicrobial peptides implicated in the resistance of epithelial surfaces to microbial colonization.

Defensins are 2 to 6 kDa, cationic, microbicidal peptides active against many Gram-negative and Gram-positive bacteria, fungi, and enveloped viruses,[1] containing three pairs of intramolecular disulfide bonds.

On the basis of their size and pattern of disulfide bonding, mammalian defensins are classified into alpha, beta and theta categories.

However, in other species, beta-defensins are more often produced by epithelial cells lining various organs (e.g. the epidermis, bronchial tree and genitourinary tract).

[5] The appearance of SNPs in the coding region will highly likely affecting the resistance against infections through changes in the protein sequences which will give rise to different biological functions.

[6] When the receptors are activated a cascade reaction will take place and substances such as cytokines and antimicrobial peptides[8] will be released.

[9] Pore complex will be created as a result of breaking the hydrogen bonds between the amino acids in the terminal end of the strands connecting defensins monomers.

Avian heterophiles can be divided into two sub-classes, depending on the number of present homologous residues in the genome.