Levels of serum ECP are elevated in TH2 engaging parasitic and helminth infections and eosinophils have long been thought to be a major defence against these types of infection. Elevated ECP have also been reported in some cases of bacterial and viral respiratory infections. Given that ECP is a cytotoxic ribonuclease, the ability of the protein to exterminate parasites, bacteria and virus in vitro has been extensively investigated (see also Figure 6 ).