No abstract

The DRB gene of the domestic cat MHC appears to be highly polymorphic, with 71 alleles provisionally reported, based on exon 2 sequence. However, these alleles were reported prior to the adoption of strict criteria for allele identification. In this study, we investigated FLA-DRB exon 2 polymorphisms in a cohort of 33 British domestic cats by polymerase chain reaction (PCR) and clonal sequence analysis. Applying the strict criteria for assigning new alleles as used by the established mammalian MHC nomenclature committees, we defined 13 FLA-DRB alleles, including four previously unreported alleles. We identified many sequences that were one or two base pairs different from these 13 defined alleles, and have shown that these are most likely artefacts of PCR amplification. When the same criteria for allele acceptance were applied to the remaining previously reported sequences, 11 further alleles were confirmed. This suggests that to date there is good evidence for 24 FLA-DRB alleles fulfilling nomenclature criteria. Analysis of these 24 alleles reveals a similar pattern of MHC polymorphism to that seen in other mammals, with three regions of hypervariability.

The clinical and epidemiological features of feline calicivirus associated vaccine reactions and breakdowns were investigated. Twenty per cent of 123 vaccine reactions were associated with acute oral/respiratory disease alone, and 80 per cent were associated with lameness either alone or in association with other clinical signs. Feline calicivirus was isolated from oropharyngeal swabs from 69 per cent of the vaccine reaction cases. Twenty-four of 31 vaccine breakdowns were associated with acute oral/respiratory disease and only seven with lameness; the virus was isolated from 28 of the 31 breakdowns. Some of the viruses isolated from the vaccine reactions were compared with the appropriate vaccine virus in virus neutralisation tests; the majority appeared to be different from the vaccine virus and were presumably field viruses. However, some appeared more similar to the vaccine virus and the majority of these were associated with lameness after the first vaccination.

Feline calicivirus (FCV) can be typed by exploiting antigenic differences between isolates or, more recently, by the sequence analysis of a hypervariable region of the virus's capsid gene. These two methods were used to characterise FCV isolates from 20 vaccine failures which occurred after the use of a commercial, live-attenuated vaccine. Using virus neutralisation, the isolates showed a spectrum of relatedness to the vaccine; depending on the criterion adopted for identity, 10 to 40 per cent of them appeared to be similar to the vaccine virus. Using sequence analysis, the isolates fell into one of two categories; 20 per cent had a similar sequence to the vaccine (0-67 to 2-67 per cent distant), and the remainder had a dissimilar sequence (21-3 to 36-0 per cent distant). Sequence analysis identified one cat that appeared to be infected with two distinct FCVs. The serological and sequence-based typing methods gave the same result in 80 to 95 per cent of individual cases, depending on the criterion adopted for serological identity. It is suggested that molecular typing is a more definitive method for characterising the relatedness of FCV isolates.

There is now considerable evidence to suggest the cheetah (Acinonyx jubatus) has limited genetic diversity. However, the extent of this and its significance to the fitness of the cheetah population, both in the wild and captivity, is the subject of some debate. This reflects the difficulty associated with establishing a direct link between low variability at biologically significant loci and deleterious aspects of phenotype in this, and other, species. Attempts to study one such region, the feline leucocyte antigen (FLA), are hampered by a general reliance on cloning and sequencing which is expensive, labour-intensive, subject to PCR artefact and always likely to underestimate true variability. In this study we have applied reference strand-mediated conformational analysis (RSCA) to determine the FLA-DRB phenotypes of 25 cheetahs. This technique was rapid, repeatable and less prone to polymerase chain reaction (PCR)-induced sequence artefacts associated with cloning. Individual cheetahs were shown to have up to three FLA-DRB genes. A total of five alleles were identified (DRB*ha14-17 and DRB*gd01) distributed among four genotypes. Fifteen cheetahs were DRB*ha14/ha15/ha16/ha17, three were DRB*ha15/ha16/ha17, six were DRB*ha14/ha16/ha17 and one was DRB*ha14/ha15/ha16/ha17/gd01. Sequence analysis of DRB*gd01 suggested it was a recombinant of DRB*ha16 and DRB*ha17. Generation of new alleles is difficult to document, and the clear demonstration of such an event is unusual. This study confirms further the limited genetic variability of the cheetah at a biologically significant region. RSCA will facilitate large-scale studies that will be needed to correlate genetic diversity at such loci with population fitness in the cheetah and other species.