Early events following bovine leukaemia virus infection in calves with different alleles of the major histocompatibility complex  DRB3 gene.

Cattle maintaining a low proviral load (LPL) status after bovine leukaemia virus (BLV) infection have been recognized as BLV controllers and non-transmitters to uninfected cattle in experimental and natural conditions. LPL has been associated with host genetics, mainly with the BoLA class II DRB3 gene. The aim of this work was to study the kinetics of BLV and the host response in Holstein calves carrying different BoLA-DRB3 alleles. Twenty BLV-free calves were inoculated with infected lymphocytes. Two calves were maintained uninfected as controls. Proviral load, total leukocyte and lymphocyte counts, anti-BLVgp51 titres and BLVp24 expression levels were determined in blood samples at various times post-inoculation. The viral load peaked at 30 days post-inoculation (dpi) in all animals. The viral load decreased steadily from seroconversion (38 dpi) to the end of the study (178 dpi) in calves carrying a resistance-associated allele (*0902), while it was maintained at elevated levels in calves with *1501 or neutral alleles after seroconversion. Leukocyte and lymphocyte counts and BLVp24 expression did not significantly differ between genetic groups. Animals with < 20 proviral copies/30 ng of DNA at 178 dpi or < 200 proviral copies at 88 dpi were classified as LPL, while calves with levels above these limits were considered to have high proviral load (HPL) profiles. All six calves with the *1501 allele progressed to HPL, while LPL was attained by 6/7 (86%) and 2/6 (33%) of the calves with the *0902 and neutral alleles, respectively. One calf with both *0902 and *1501 developed LPL. This is the first report of experimental induction of the LPL profile in cattle.

Forletti A ，Lützelschwab CM ，Cepeda R ，Esteban EN ，Gutiérrez SE ... -  《-》

Co-infection with Mycobacterium bovis does not alter the response to bovine leukemia virus in BoLA DRB3*0902, genetically resistant cattle.

High proviral load (HPL) profile in bovine leukemia virus infected animals poses increased risk of transmission, and development of HPL or low proviral load (LPL) profile may be attributed to host genetics. Genetic resistance and susceptibility has been mapped to the Major Histocompatibility Complex class II DRB3 gene (BoLA DRB3). The aim of this work was to determine the effect of Mycobacterium bovis infection on certain virological and host immunological parameters of BLV experimental infection. Twenty-six Argentinian Holstein calves carrying the resistance-associated marker allele BoLA DRB3*0902, susceptibility-associated marker allele BoLA DRB3*1501, or neutral BoLA DRB3 alleles, exposed to M. bovis were used. Twenty calves were inoculated with BLV, three were naturally infected and other three were BLV-negative. Seven from twenty six (27%) of the animals resulted positive to the PPD test. The proviral load, absolute leukocyte and lymphocyte counts, time to seroconversion, antibody titer against BLV, and viral antigen expression in vitro at various times post inoculation were determined and compared between PPD+ and PPD- animals. From a total of 23 BLV positive animals (naturally and experimentally infected), 13 (56.5%) developed HPL, and 10 (43.5%) developed LPL. None of the investigated parameters were affected by infection with M. bovis. We concluded that the ability of cattle carrying resistance-associated marker to control BLV and to progress towards a LPL phenotype was not altered by M. bovis co-infection.

Lützelschwab CM ，Forletti A ，Cepeda R ，Esteban EN ，Confalonieri O ，Gutiérrez SE ... -  《-》

Identification of bovine leukocyte antigen class II haplotypes associated with variations in bovine leukemia virus proviral load in Japanese Black cattle.

Bovine leukemia virus (BLV) is the etiological agent of enzootic bovine leukosis, which is the most common neoplastic disease of cattle. Bovine leukocyte antigen (BoLA) is strongly involved in the subclinical progression of BLV infections. Recent studies show that the BoLA-DRB3 gene might play a direct role in controlling the number of BLV-infected peripheral B lymphocytes in vivo in Holstein cattle. However, the specific BoLA class II allele and DRB3-DQA1 haplotypes determining the BLV proviral load in Japanese Black cattle are yet to be identified. In this study, we focused on the association of BLV proviral load and polymorphism of BoLA class II in Japanese Black cattle. We genotyped 186 BLV-infected, clinically normal cattle for BoLA-DRB3 and BoLA-DQA1 using a polymerase chain reaction-sequence-based typing method. BoLA-DRB3*0902 and BoLA-DRB3*1101 were associated with a low proviral load (LPVL), and BoLA-DRB3*1601 was associated with a high proviral load (HPVL). Furthermore, BoLA-DQA1*0204 and BoLA-DQA1*10012 were related to LPVL and HPVL, respectively. Furthermore, we confirmed the correlation between the DRB3-DQA1 haplotype and BLV proviral load. Two haplotypes, namely 0902B or C (DRB3*0902-DQA1*0204) and 1101A (DRB3*1101-DQA1*10011), were associated with a low BLV proviral load, whereas one haplotype 1601B (DRB3*1601-DQA1*10012) was associated with a high BLV proviral load. We conclude that resistance is a dominant trait and susceptibility is a recessive trait. Additionally, resistant alleles were common between Japanese Black and Holstein cattle, and susceptible alleles differed. This is the first report to identify an association between the DRB3-DQA1 haplotype and variations in BLV proviral load.

Miyasaka T ，Takeshima SN ，Jimba M ，Matsumoto Y ，Kobayashi N ，Matsuhashi T ，Sentsui H ，Aida Y ... -  《-》

Association of BLV infection profiles with alleles of the BoLA-DRB3.2 gene.

Bovine leukaemia virus (BLV) causes lymphosarcoma and persistent lymphocytosis (PL). Some MHC class II gene polymorphisms have been associated with resistance and susceptibility to the development of lymphosarcoma and PL, as well as with a reduced number of circulating BLV-infected lymphocytes. Previously, 230 BLV-infected Holstein cattle were classified into two infection profiles characterized by low and high proviral loads (LPL and HPL respectively). Here, the influence of the polymorphism at the BoLA-DRB3.2* gene of these animals was examined. After genotyping, the association between the BoLA-DRB3.2* alleles and the BLV infection profile was determined as the odds ratio (OR). Two subtypes of allele *11 were identified (ISAG*0901 and *0902). Allele ISAG*0902 showed a stronger association with the LPL profile (OR = 8.24; P < 0.0001) than allele *11 itself (OR = 5.82; P < 0.0001). Allele ISAG*1701 (*12) also showed significant association with the LPL profile (OR = 3.46; P < 0.0055). Only one allele, ISAG*1501 or 03 (*16), showed significant association with HPL (OR = 0.36; P < 0.0005). The DRB3.2* alleles were assigned to three categories: resistant (R), susceptible (S) and neutral (N). Based on their DRB3 genotypes, cattle were classified as homozygous or heterozygous. The RR and RN genotypes were associated with the LPL profile, while the SS and NS genotypes were associated with the HPL profile. The RS genotype could not be associated with any particular profile. Our results show that allele ISAG*0902 appears to be the best BLV resistance marker in Holstein cattle.

Juliarena MA ，Poli M ，Sala L ，Ceriani C ，Gutierrez S ，Dolcini G ，Rodríguez EM ，Mariño B ，Rodríguez-Dubra C ，Esteban EN ... -  《-》

Cattle with the BoLA class II DRB3*0902 allele have significantly lower bovine leukemia proviral loads.

The bovine MHC (BoLA) class II DRB3 alleles are associated with polyclonal expansion of lymphocytes caused by bovine leukemia virus (BLV) infection in cattle. To examine whether the DRB3*0902 allele, one of the resistance-associated alleles, is associated with the proviral load, we measured BLV proviral load of BLV-infected cattle and clarified their DRB3 alleles. Fifty-seven animals with DRB3*0902 were identified out of 835 BLV-infected cattle and had significantly lower proviral load (P<0.000001) compared with the rest of the infected animals, in both Japanese Black and Holstein cattle. This result strongly indicates that the BoLA class II DRA/DRB3*0902 molecule plays an important immunological role in suppressing viral replication, resulting in resistance to the disease progression.

Hayashi T ，Mekata H ，Sekiguchi S ，Kirino Y ，Mitoma S ，Honkawa K ，Horii Y ，Norimine J ... -  《-》