H. Takahashi et al., NUCLEOTIDE-SEQUENCE ANALYSIS OF HUMAN T-CELL LEUKEMIA-VIRUS, TYPE-II (HTLV-II) ISOLATES, AIDS research and human retroviruses, 9(8), 1993, pp. 721-732
A study by Hall et al. (J Virol 1992;66:2456-2463; Ref. 11) has sugges
ted the existence of two closely related molecular subtypes of HTLV-II
, which were tentatively designated HTLV-IIa and HTLV-IIb. To confirm
this nucleotide sequence analysis of 986 bp of the env gene region enc
oding the entire surface glycoprotein, gp46, and the amino terminus of
the transmembrane glycoprotein, gp21, of 10 HTLV-II isolates was carr
ied out. The results clearly established the existence of two subtypes
and demonstrated a 4.3% divergence in sequence in this region. Analys
is of other gene regions of the provirus, including the pol (1544 bp),
gag (448 bp), and the entire LTR (743 bp) of two representative isola
tes of each subtype, showed a sequence divergence of 3.8 to 5.7%, with
greatest divergence occurring in the LTR. In addition to single nucle
otide changes, the gag regions encoding the structural protein, p19, o
f the HTLV-IIb isolates were also found to have a 66-bp deletion that
would be expected to result in a p19 protein having a 22-amino acid de
letion in the carboxy-terminus region. Attempts to exploit this to dif
ferentiate the two subtypes serologically were unsuccessful in that re
combinant p19 proteins of both subtypes were found to be antigenically
cross-reactive. The finding of two molecular subtypes of HTLV-II may
have important implications for a better understanding of the biologic
al and pathogenic properties of the virus, and will be useful in chara
cterizing the viruses present in endemic foci in American Indian popul
ations.