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Role of Env in Resistance of Feline Immunodeficiency Virus (FIV)-Infected Cats to Superinfection by a Second FIV Strain as Determined by Using a Chimeric Virus

Retrovirus Center and Virology Section, Department of Experimental Pathology, University of Pisa, I-56127 Pisa,¹ Department of Public Health, University of Florence, I-50134 Firenze, Italy²

Received 17 May 2007/ Accepted 9 July 2007

A more or less pronounced resistance to superinfection by a second strain of the infecting virus has been observed in many lentivirus-infected hosts. We used a chimeric feline immunodeficiency virus (FIV), designated FIV, containing a large part of the env gene of a clade B virus (strain M2) and all the rest of the genome of a clade A virus (a p34TF10 molecular clone of the Petaluma strain modified to grow in lymphoid cells), to gain insights into such resistance. FIV was infectious and moderately pathogenic for cats and in vitro exhibited the neutralization specificity of the env donor. The experiments performed were bidirectional, in that cats preinfected with either parental virus were challenged with FIV and vice versa. The preinfected animals were partially or completely protected relative to what was observed in naïve control animals, most likely due, at least in part, to the circumstance that in all the preinfecting/challenge virus combinations examined, the first and the second virus shared significant viral components. Based on the proportions of complete protection observed, the role of a strongly matched viral envelope appeared to be modest and possibly dependent on the time interval between the first and the second infection. Furthermore, complete protection and the presence of measurable neutralizing antibodies capable of blocking the second virus in vitro were not associated.

Published ahead of print on 18 July 2007.