Failure to isolate human T cell lymphotropic virus type I and to detect variant-specific genomic sequences by polymerase chain reaction in Melanesians with indeterminate Western immunoblot

1 Laboratory of Central Nervous System Studies, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, U.S.A. 2 Ministry of Health and Medical Services, Central Hospital, Honiara, Solomon Islands and 3 Papua New Guinea Institute of Medical Research, Goroka, Papua New Guinea The controversy over the endemicity of human T cell lymphotropic virus type I (HTLV-I) in Melanesia has been settled recently by the isolation of genetically distinct, highly divergent sequence variants of HTLV-I from unrelated inhabitants of Papua New Guinea and the Solomon Islands. Still at issue, however, is the significance of the high frequency of indeterminate HTLV-I Western blots (defined as reactivity to only gag -encoded proteins) among Melanesians. To investigate whether this indeterminate seroreactivity reflects specific reactivity to the Melanesian HTLV-I variants, 27 seroindeterminate Melanesians from Papua New Guinea and the Solomon Islands were studied for evidence of HTLV-I infection. Although antibodies against Melanesian variant-specific env gene products and variant-specific env gene sequences were detected by Western blot analysis and polymerase chain reaction, respectively, in all 11 HTLV-I Western blot-positive Melanesians, none of the 27 seroindeterminate Melanesians had such variant-specific antibodies or HTLV-I proviral sequences. In addition, attempts to isolate HTLV-I from seroindeterminate individuals were unsuccessful. These data indicate that HTLV-I infection is not the cause of the indeterminate Western blot reactivity seen in Melanesia. Received 21 January 1992; accepted 17 March 1992.