EWA BJORLING 1. INTRODUCTION
Human immunodeficiency virus type 2 (HIV-2), the second type of lenti-virus discovered to cause immunodeficiency in humans, was first isolated from a West African patient.1-3 HIV-2 infection has been documented in Africa, Europe, the Americas, and Asia, but is still mostly confined to West Africa and Portugal. Since HIV-2 has a more restricted geographic distribution and a somewhat reduced disease-causing potential, research involving HIV-2 has been less extensive when compared with the globally occurring HIV-1.
The primate lentiviruses are classified according to their phylogenetic relationships, which have been determined by comparing their nucleotide sequences. The most common approach is to assess how often particular clusters of sequences occur when the data are randomly resampled.4 The classification of a phylogenetic tree of primate lentiviruses leads to a first level of different lineages, and the second level of classification is to identify subgroups within each of these clusters.5-9
HIV-2 has been divided into several different subtypes, and nearly all of them have been identified in West Africa. More recently, epidemic spreading of HIV-2 subtype A isolates was demonstrated in India. The most common subtypes today are A and B, which are both prevalent throughout West Africa, while the other subtypes are only represented by a few isolates.
HIV-2, like other lentiviruses, has the capacity to direct the synthesis of a large number of different proteins, of which some are important for the
EWA BJORLING • Microbiology and Tumorbiology Center, Karolinska Institute, S171 77 Stockholm, Sweden.
Human Retroviral Infections, edited by Kenneth E. Ugen et al. Kluwer Academic / Plenum Publishers, New York, 2000.
formation of the virus particles, whereas other proteins of a nonstructural nature appear in infected cells and may be released through secretion by the cell. Each of these proteins has immunogenic sites which may elicit cellmediated and humoral immune responses. For an extended knowledge of HIV immunobiology and development of treatment against acquired immune deficiency syndrome (AIDS) it is therefore necessary to obtain a comprehensive understanding of the dynamics and specificities of these immune reactions.
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