Little is known concerning guard receptors in humans. One example currently under speculation involves recognition of cysteine proteases secreted by helminths during infection.[16] It has been speculated that some allergies develop as a result of structural similarities between the allergen and high-activity cysteine proteases secreted by helminths during their infectious cycle.[17] One proposed mechanism by which this may take place is that proteases secreted by the helminths cleave proteins which act as detectors, and these detectors in turn activate sensors to alert the immune system.[18]