RESUMEN
Cowdria ruminantium causes the tick-borne rickettsial disease of heartwater, which is devastating to livestock production in sub-Saharan Africa. Current diagnosis and control methods are inadequate. We have identified and sequenced a subset of genes encoding recombinant antigens recognized by antibody and peripheral blood mononuclear cells from immune ruminants. The identified genes include many with significant similarity to those of Rickettsia prowazekii, genes predicted to encode different outer membrane proteins and lipoproteins and a gene containing an unusual tandem repeat structure. Evidence is presented for immune protection by recombinant antigens in a mouse model of C. ruminantium infection. These data identify new recombinant antigens for evaluation in vaccines and diagnostic tests to control heartwater.
Asunto(s)
Ehrlichia ruminantium/genética , Genes Bacterianos/genética , Sistema Inmunológico/inmunología , Animales , Proteínas Bacterianas/genética , Proteínas Bacterianas/inmunología , Vacunas Bacterianas/inmunología , Bovinos , División Celular/inmunología , Sistema Libre de Células/metabolismo , ADN Bacteriano/química , ADN Bacteriano/genética , ADN Bacteriano/aislamiento & purificación , Ehrlichia ruminantium/inmunología , Hidropericardio/inmunología , Hidropericardio/microbiología , Hidropericardio/mortalidad , Sueros Inmunes/inmunología , Sistema Inmunológico/microbiología , Linfocitos/citología , Linfocitos/inmunología , Linfocitos/microbiología , Ratones , Datos de Secuencia Molecular , Biosíntesis de Proteínas , Análisis de Secuencia de ADN , Ovinos , Tasa de Supervivencia , Transcripción GenéticaRESUMEN
Anaplasma marginale is a rickettsial parasite of bovine erythrocytes causing world-wide economic losses in livestock production. Despite its importance, little is known about this rickettsia at a molecular level because it has not been cultured in vitro, and there is no small-animal model. Although several genes have been cloned and sequenced, the gross genome structure of the organism has not yet been well characterized. We separated intact bovine erythrocytes from leucocytes, and determined the genome size of A. marginale by use of restriction endonuclease cleavage and pulsed-field gel electrophoresis (PFGE). A value of 56 mol% G+C was obtained for this genome by spectral analysis. Undigested A. marginale DNA failed to migrate under several different electrophoretic conditions, indicating a circular genome. Digestions of intact A. marginale DNA were performed using restriction endonucleases NotI, SfiI and PacI. Complete digestion with SfiI resulted in 12 distinct bands ranging in size from 14 to 170 kbp. Total size determined by addition of SfiI-digested fragments was approximately 1200 kbp. PacI cleaved the A. marginale genome from three different isolates into just three fragments, of 598, 557 and 97 kbp. Incomplete digestion produced a band measuring 1250 kbp. These results indicate that A. marginale has a circular genome between 1200 and 1260 kbp, with a G+C content of 56 mol%.
Asunto(s)
Anaplasma/genética , Electroforesis en Gel de Campo Pulsado/veterinaria , Genoma Bacteriano , Anaplasmosis/sangre , Anaplasmosis/genética , Animales , Composición de Base , Bovinos , Nucleótidos de Citosina/análisis , Eritrocitos/química , Eritrocitos/microbiología , Nucleótidos de Guanina/análisis , Polimorfismo de Longitud del Fragmento de RestricciónRESUMEN
African trypanosomes possess several elegant ways to evade the immune defenses o f mammalian hosts. They have an extensive repertoire o f genes for a variant surface antigen and recent data show that this finite repertoire can be further amplified by mosaic gene formation and point mutation, producing an almost limitless capacity to vary. The significance of these mechanisms of antigenic diversity to trypanosome biology and the parasite-host relationship in general are discussed here by Anthony Barbet and Sondra Kamper.
RESUMEN
Trypanosoma brucei evades the immune response of its mammalian host by antigenic variation in the major surface antigen (the variable surface glycoprotein or VSG). We examined the generation of diversity in 4 in vivo-derived antigenically related clones of T. brucei by sequencing VSG cDNA from each of the 4 clones and all 5 related genomic copies in the WaTat 1.1 progenitor organism. Each expressed VSG gene was a different mosaic of basic copy genes; 3 were complex mosaics consisting of multiple fragments from at least 3 basic copy genes. All 4 basic copy genes were involved in mosaic gene formation even though at least 2 were pseudogenes. Point mutations were a minor component to VSG variability. We conclude that, in vivo, expression of mosaic VSG genes amplifies the effective surface antigen repertoire of T brucei. We propose that this additional source of antigenic variation is crucial to long term survival of the parasite in its mammalian host, and may be the primary function of VSG multigene families in trypanosomes.