Macrophage inflammatory protein-1 alpha (MIP-1 alpha) is a chemokine that leads to leukocyte recruitment and activation at sites of infection. Controlling chemokine activity at sites of infection is important, since excess accumulation of leukocytes may contribute to localized tissue damage. Neutrophil-derived serine proteases modulate the bioactivity of chemokine and cytokine networks through proteolytic cleavage. Because MIP-1 alpha is temporally expressed with neutrophils at sites of infection, we examined proteolysis of MIP-1 alpha in vitro by the neutrophil-derived serine proteases: cathepsin G, elastase, and proteinase 3. Recombinant human MIP-1 alpha isoforms LD78 beta and LD78 alpha were expressed and purified, and the protease cleavage sites were analyzed by mass spectrometry and peptide sequencing. Chemotactic activities of parent and cleavage molecules were also compared. Both LD78 beta and LD78 alpha were cleaved by neutrophil lysates at Thr(16)- Ser(17), Phe(24)- Ile(25), Tyr(28)- Phe(29), and Thr(31)-Ser(32). This degradation was inhibited by serine protease inhibitors phenylmethylsulfonyl fluoride and 4-(2-aminoethyl)-benzenesulfonyl fluoride. Incubation of the substrates with individual proteases revealed that cathepsin G preferentially cleaved at Phe24- Ile25 and Tyr28- Phe29, whereas elastase and proteinase 3 cleaved at Thr(16)- Ser(17) and Thr(31)- Ser(32). Proteolysis of LD78 beta resulted in loss of chemotactic activity. The role of these proteases in LD78 beta and LD78 alpha degradation was confirmed by incubation with neutrophil lysates from Papillon-Lefevre syndrome patients, demonstrating that the cell lysates containing inactivated serine proteases could not degrade LD78 beta and LD78 alpha. These findings suggest that severe periodontal tissue destruction in Papillon-Lefevre syndrome may be related to excess accumulation of LD78 beta and LD78 alpha and dysregulation of the microbial-induced inflammatory response in the periodontium.