The present invention provides nucleotide and amino acid sequences that identify and encode a new cathepsin C homolog (RCP) expressed in THP-1 cells. The present invention also provides for antisense molecules to the nucleotide sequences which encode RCP, expression vectors for the production of purified RCP, antibodies capable of binding specifically to RCP, hybridization probes or oligonucleotides for the detection of RCP-encoding nucleotide sequences, genetically engineered host cells for the expression of RCP, diagnostic tests for activation of monocyte/macrophages based on RCP-encoding nucleic acid molecules, and use of the protein to produce antibodies capable of binding specifically to the protein and use of the protein to screen for inhibitors.