ABSTRACT
Naegleria fowleri, the causative agent of primary amebic meningoencephalitis, is resistant to complement lysis. The presence of a complement regulatory protein on the surface of N. fowleri was investigated. Southern blot and Northern blot analyses demonstrated hybridization of a radiolabeled cDNA probe for CD59 to genomic DNA and RNA, respectively, from pathogenic N. fowleri. An 18-kDa immunoreactive protein was detected on the membrane of N. fowleri by Western immunoblot and immunofluorescence analyses with monoclonal antibodies for human CD59. Complement component C9 immunoprecipitated with the N. fowleri "CD59-like" protein from amebae incubated with normal human serum. In contrast, a gene or protein similar to CD59 was not detected in nonpathogenic, complement-sensitive N. gruberi amebae. Collectively, our studies suggest that a protein reactive with antibodies to human CD59 is present on the surface of N. fowleri amebae and may play a role in resistance to lysis by cytolytic proteins.
Subject(s)
Antibodies, Monoclonal/immunology , CD59 Antigens , Membrane Proteins , Naegleria fowleri/pathogenicity , Protozoan Proteins , Amebiasis/parasitology , Animals , Antibodies, Monoclonal/metabolism , Antibodies, Protozoan/genetics , Antibodies, Protozoan/immunology , Antibodies, Protozoan/metabolism , CD59 Antigens/genetics , CD59 Antigens/immunology , CD59 Antigens/metabolism , Cell Line , Complement C9 , Cross Reactions , Humans , Immunoprecipitation , Membrane Proteins/genetics , Membrane Proteins/immunology , Membrane Proteins/metabolism , Meningoencephalitis/parasitology , Naegleria fowleri/metabolism , Protozoan Proteins/genetics , Protozoan Proteins/immunology , Protozoan Proteins/metabolismABSTRACT
Found in soil and freshwater habitats, Naegleria fowleri are free-living amebae that cause a fatal disease in humans called Primary Amebic Meningoencephalitis. In the natural environment, amebae feed on bacteria. In the infected host, the amebae lyse and ingest nerve tissue. Recently, we have established that N. fowleri expresses a "CD59-like" surface protein, but the function of this protein in the ameba has not been elucidated. In mammalian cells, CD59 is a complement-regulatory protein that inhibits complement-mediated lysis of cells expressing this protein. In the present study, expression of the "CD59-like" protein in response to bacteria and bacterial toxins was investigated by Western immunoblot analysis. Co-culture of N. fowleri with log phase Escherichia coli or Pseudomonas aeruginosa resulted in differential expression of the "CD59-like" protein. Co-cultures of amebae and bacteria were examined by electron microscopy. The results of our study implicate a possible protective role of the "CD59-like" protein in response to bacterial predators and bacterial toxins, because amebae remained intact after co-culture with bacteria.
