Human eosinophils are activated by cysteine proteases and release inflammatory mediators.
BACKGROUND
Recent studies suggest that serine proteases are involved in various biological responses through activation of protease-activated receptors (PARs). However, the functions of other proteases, such as cysteine proteases, are poorly understood and need elucidation.


OBJECTIVE
We examined the effects of an authentic cysteine protease, papain, and a protease derived from the mite allergen, Der f 1, on functions of human eosinophils.


METHODS
Purified eosinophils were incubated with papain or Der f 1. Eosinophil activation was monitored by superoxide anion generation and by degranulation. Intracellular signaling pathways were investigated through use of pharmacologic approaches.


RESULTS
We found that papain potently induces human eosinophils to degranulate and to produce superoxide anion. A cysteine protease inhibitor, E-64, abolished the stimulatory effects of papain, which suggests that the protease activity of papain is necessary to trigger eosinophil responses. The eosinophil's response to papain was enhanced by IL-5 and mediated by activation of the phosphatidylinositol 3-kinase/Akt pathway. Interestingly, whereas a serine protease, trypsin, activated eosinophils through PAR2, the effects of papain were not inhibited by an antibody to PAR2, which suggests another novel mechanism for the eosinophils' response to cysteine proteases. It is likely that these observations are clinically important, because eosinophils were activated by a natural cysteine protease allergen, Der f 1, and released granule proteins.


CONCLUSIONS
Human eosinophils are probably equipped with machineries that recognize and respond to cysteine proteases, such as those found at allergic inflammation sites; the result is active release of proinflammatory mediators.
Miike
Satoshi
S
Department of Medicine (Division of Allergic Diseases), Mayo Clinic Rochester, MN 55905, USA.
Kita
Hirohito
H
D039741:Antigens, Dermatophagoides / Q000494:pharmacology; D060829:Arthropod Proteins; D003546:Cysteine Endopeptidases / Q000494:pharmacology*; D004804:Eosinophils / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D018836:Inflammation Mediators / Q000378:metabolism*; D015848:Interleukin-5 / Q000494:pharmacology; D010206:Papain / Q000494:pharmacology; D011493:Protein Kinase C / Q000502:physiology; D044464:Receptor, PAR-2; D018179:Receptors, Thrombin / Q000502:physiology; D013481:Superoxides / Q000378:metabolism
D039741:Antigens, Dermatophagoides; D060829:Arthropod Proteins; D018836:Inflammation Mediators; D015848:Interleukin-5; D044464:Receptor, PAR-2; D018179:Receptors, Thrombin; D013481:Superoxides; D011493:Protein Kinase C; D003546:Cysteine Endopeptidases; C451159:Dermatophagoides farinae antigen f 1; D010206:Papain