The three different pore-forming RTX-toxins of Actinobacillus pleuropneumoniae are reviewed, and new and uniform designations for these toxins and their genes are proposed. The designation ApxI (for &tinobacillus pZeuropneumoniae RTX-toxin I) is proposed for the RTX-toxin produced by the reference strains for serotypes 1, 5a, 5b, 9,lO and 11, which was previously named haemolysin I (HlyI) or cytolysin I (ClyI). This protein is strongly haemolytic and shows strong cytotoxic activity towards pig alveolar macrophages and neutrophils; it has an apparent molecular mass in the range 105 to 110 kDa. The genes of the apxZ operon will have the designations apxZC, apxZA, apxZB, and apxZD for the activator, the structural gene and the two secretion genes respectively. The designation ApxII is proposed for the RTX-toxin which is produced by all serotype reference strains except serotype 10 and which was previously named App, HlyII, ClyII or Cyt. This protein is weakly haemolytic and moderately cytotoxic and has an apparent molecular m a s between 103 and 105 kDa. The genes of the apxZZ operon will have the designations apxZZC for the activator gene and apxZZA for the structural toxin gene. In the apxZZ operon, no genes for secretion proteins have been found. Secretion of ApxII seems to occur via the products of the secretion genes apxZB and apxZD of the apxZ operon. The designation ApxIII is proposed for the nonhaemolytic RTX-toxin of the reference strains for serotypes 2, 3, 4, 6 and 8, which was previously named cytolysin 111 (ClyIII), pleurotoxin (Ptx), or macrophage toxin (Mat). This protein is strongly cytotoxic and has an apparent molecular mass of 120 kDa. The genes of the apxZZZ operon have the designations apxZZZC, apxZZZA, apxZZZB and apxZZZD for the activator gene, the structural gene and the two secretion genes respectively.

No abstract

Mutants of Actinobacilluspleuropneumoniue strain HK 361 (serotype 2) were isolated which were deficient in type I1 (Ca2+-dependent) haemolysin activity (Hly-). Some of the Hly-mutants secreted a potent, heat-labile extracellular cytotoxic activity against porcine alveolar macrophages. Comparison of cell-free culture supernatant from the parent strain and some Hly-mutants by SDS-PAGE and immunoblotting revealed the loss of a major extracellular polypeptide of 109 kDa. Two Hly-mutants which in addition failed to secrete a 120 kDa polypeptide produced no extracellular cytotoxic activity, suggesting that the 120 kDa protein was the cytotoxin. Antiserum raised to the culture supernatant from a Hly-mutant lacking the 109 kDa polypeptide recognized the 120 kDa band, but not the 109 kDa band, in immunoblots and neutralized the cytotoxic activity, but not the haemolytic activity, of A. pleuropneumoniue. The 120 kDa polypeptide and extracellular cytotoxic activity were widespread among A. pleuropneumoniue strains, but absent from related bacterial pathogens of the pig: Actinobacillus suis, Huemophilus purusuis and Pusteurellu multocidu. A clear correlation was found between the presence of the 120 kDa pdypeptide'and cytotoxic activity in culture supernatants. The cytotoxic activity of all the strains tested was neutralized by antibody to the Hly-extracellular material and by convalescent pig serum. It is proposed that the 120 kDa polypeptide represents the cytotoxin of A. pleuropneumonia?, that it is distinct from the haemolysin, and that it be termed pleurotoxin.

It has been shown that cats can be protected against infection with the prototypic Petaluma strain of feline immunodeficiency virus (FIV PET ) using vaccines based on either inactivated virus particles or replicationdefective proviral DNA. However, the utility of such vaccines in the field is uncertain, given the absence of consistent protection against antigenically distinct strains and the concern that the Petaluma strain may be an unrepresentative, attenuated isolate. Since reduction of viral pathogenicity and dissemination may be useful outcomes of vaccination, even in the absence of complete protection, we tested whether either of these vaccine strategies ameliorates the early course of infection following challenge with heterologous and more virulent isolates. We now report that an inactivated virus vaccine, which generates high levels of virus neutralizing antibodies, confers reduced virus loads following challenge with two heterologous isolates, FIV AM6 and FIV GL8 . This vaccine also prevented the marked early decline in CD4/CD8 ratio seen in FIV GL8 -infected cats. In contrast, DNA vaccines based on either FIV PET or FIV GL8 , which induce cell-mediated responses but no detectable antiviral antibodies, protected a fraction of cats against infection with FIV PET but had no measurable effect on virus load when the infecting virus was FIV GL8 . These results indicate that the more virulent FIV GL8 is intrinsically more resistant to vaccinal immunity than the FIV PET strain and that a broad spectrum of responses which includes virus neutralizing antibodies is a desirable goal for lentivirus vaccine development.

Ten-fold serial dilutions of the H52 vaccine strain of infectious bronchitis virus were inoculated intravenously into 3-week-old and 10-week-old chickens. The severity of the histological lesions in the kidney was graded and described. The younger birds were much more resistant to the nephritogenic effects of the virus. Although very small doses of virus caused nephritis, no marked dose-related response was demonstrated in either age group.