Antimicrobial peptides are natural peptides secreted by the epithelial cells and phagocytes. There are various types of antimicrobial peptides such as Defensins, Cathelicidens and Lysozymes. Defensins are of three main types, Alpha and Beta and Theta with alpha and beta defensins mainly found mainly in mammals. Defensins have a broad spectrum of activity against microorganisms which is achieved in various ways including distortion of the microbial membrane by forming pores or transient gaps leading to release of cellular contents and influx of water resulting in the lysis of the cell. In the study, the opsonizing ability of the Beta defensin 2 was investigated. This was demonstrated by measuring the respiratory burst of two cell lines, Thp-1 and U937 which were activated with various stimulants including the Beta defensin 2 treated bacteria. The respiratory burst was analyzed with the use of oxygen electrode apparatus. The study revealed a variety of results with Thp-1 cell line utilizing more oxygen than expected due to a possible early activation by contaminants in the sample or apparatus used. A slightly lower oxygen consumption was utilized by the U937 cell line although it was still higher than the other more potential cell line activating samples. The penicillin treated bacteria yielded a low oxygen consumption rate in both cell lines suggesting that the cell lines could have been partially dead or required more time for activation in the presence of the antibiotic treated bacteria. The Chloramphenicol treated bacteria in both cell lines consumed more oxygen indicating that the cell lines recognized the bacteria by possibly attaching to a surface protein on the bacteria. The heat killed bacteria which was only assessed in the case of Thp-1 cell line did not prove to stimulate a significant number of the cell line which could be due to the fact that macrophages phagocytose dead bacterial cells slowly compared to live bacterial cells. Finally, the cell line in the presence of beta defensin 2 were analyzed to have a respiratory burst rate higher than the rest suggesting a possible ability of beta defensin 2 to opsonize bacteria for the cell lines

Keywords : Beta Defensin 2; Opsonin; Oxygen consumption; THP cell line.