Immunoglobulin A1 Protease, an Exoenzyme of Pathogenic Neisseriae, Is a Potent Inducer of Proinﬂammatory Cytokines By Dirk R. Lorenzen, Frank Düx, Uwe Wölk, Anastasios Tsirpouchtsidis, Gaby Haas, and Thomas F. Meyer From the Max-Planck-Institut für Infektionsbiologie, Abteilung Molekulare Biologie, 10117 Berlin, Germany Summary A characteristic of human pathogenic Neisseriae is the production and secretion of an immuno- globulin (Ig)A1-specific serine protease (IgA1 protease) that cleaves preferentially human IgA1 and other target proteins. Here we show a novel function for native IgA1 protease, i.e., the induction of proinflammatory cytokines such as tumor necrosis factor (TNF)-a, interleukin (IL)-1b, IL-6, and IL-8 from peripheral blood mononuclear cells. The capacity of IgA1 pro- tease to elicit such cytokine responses in monocytes was enhanced in the presence of T lym- phocytes. IgA1 protease did not induce the regulatory cytokine IL-10, which was, however, found in response to lipopolysaccharide and phytohemagglutinin. The immunomodulatory ef- fects caused by IgA1 protease require a native form of the enzyme, and denaturation abolished cytokine induction. However, the proteolytic activity is not required for the cytokine induc- tion by IgA1 protease. Our results indicate that IgA1 protease exhibits important immunostim- ulatory properties and may contribute substantially to the pathogenesis of neisserial infections by inducing large amounts of TNF-a and other proinflammatory cytokines. In particular, IgA1 protease may represent a key virulence determinant of bacterial meningitis. Key words: Neisseria gonorrhoeae • Neisseria meningitidis • inﬂammation • tumor necrosis factor a • virulence factor T which primarily colonize human mucosal surfaces. Be- he Neisseriae are gram-negative, diplococcal bacteria sides several commensal species, the genus includes two hu- man pathogens, Neisseria gonorrhoeae (gonococci), the causative agent of gonorrhea, and Neisseria meningitidis (meningococci), one major cause of bacterial meningitis. Both pathogens exclusively colonize or infect humans as their natural hosts. Gonococci induce a local inflammatory response of the urogenital mucosa (1). Meningococci are mostly harmless colonizers of the respiratory tract (e.g., nasopharynx). Un- der some not yet fully understood circumstances, meningo- cocci disseminate from locally infected tissues into the blood stream and penetrate the blood–brain barrier to cause severe inflammations in the central nervous system (2). Various bacterial components have been implicated in the pathogenesis of neisserial infections (3–6). Pili and Opa proteins contribute to the attachment and the invasion of different host cells, and the outer membrane porin protein I or PorB was found to prevent the microbicidal activities of phagocytes (7, 5) and to induce apoptosis in target cells (8). Circumstantial evidence related to the unique association of IgA1 proteases with human pathogenic bacterial species (9, 6) suggests that this enzyme plays a significant role in pathogenesis. IgA1 proteases are produced by a variety of gram-positive and gram-negative human pathogens (10–12). Among those, the IgA1 proteases of the pathogenic Neisse- riae and various Haemophilus species are structurally closely related (13, 14). They undergo frequent horizontal exchange across the species barrier, thus forming a polymorphic class of proteins (15, 16). The gram-negative bacterial IgA1 pro- teases are derived from a polyprotein precursor molecule which directs enzyme secretion by an autocatalytic process. While the neisserial IgA1 protease precursors include two additional secreted domains, an a-protein and a g-peptide (13), the proteases of the two species probably exhibit sim- ilar functions. IgA1 protease cleaves human IgA1 both in serum and at mucosal surfaces of the respiratory and urogenital tracts (10, 17). In particular, the neisserial IgA1 protease is a sequence- specific endopeptidase which cleaves single peptide bonds of distinct proline-rich consensus sequences that are found in the hinge region of human IgA1 but not IgA2 (10, 18). As a consequence, the enzymatic activity or characteristic cleavage products of IgA1 molecules were found in na- sopharyngeal and vaginal secretions of individuals infected with pathogenic Neisseriae (11, 19, 20). As intact IgA1 pro- tects against microorganisms infecting mucosal tissues by prevention of microbial adherence, toxin neutralization, 1049 J. Exp. Med. The Rockefeller University Press • 0022-1007/99/10/1049/10 $5.00 Volume 190, Number 8, October 18, 1999 1049–1058 http://www.jem.org