**4. Genetic structure of β-defensin-2**

The gene codify for HBD2 is located on chromosome 8p23. The gene is approximately 4 kb and composed of a 5'and 3' non-translatable region, two exons separated by an intron. The first exon has 81 bp and codes for the signal peptide and the second exon has 238 bp and codes for a short anion segment called propeptide and the mature peptide [3, 25, 42]. The 5′ region of HBD2 has specific sites that bind to the transcription factor kB (NF-kB). In addition, there are sites that bind to other transcription factors such as C/EBP, and NF-IL-6, which are important for their expression [42–44].

The HBD2 have a polymorphic nature, and the number of copies of the gene varies in each individual [45]. It has been reported that there are 2–12 copies per diploid genome, and the number of copies is related to the level of expression. It has been suggested that these variations may have consequences on the function of immune system. Some infectious and inflammatory diseases are related to the number of copies of the HBD2 gene [44, 46] (**Figure 2**).

#### **Figure 2.**

*Genetic structure of HBD2. It encompasses untranslated 5 'and 3' regions and two exons separated by an intron. The first exon codes for the signal peptide and the second exon codes for the propeptide and the mature peptide [3].*
