Norbert Bannert

Cutting Edge: CD4 Is Not Required for the Functional Activity of IL-16

IL-16 functions as a chemoattractant factor, inhibitor of HIV replication, and inducer of proinflammatory cytokine production. Previous studies have suggested that CD4 is the receptor for IL-16, because only CD4+ cells respond to IL-16 and both the anti-CD4 Ab OKT4 and soluble CD4 can block IL-16 function. However, these are only indirect evidence of a requirement for CD4, and to date a direct interaction between IL-16 and CD4 has not been shown. In this paper, we report that cells from CD4 knockout mice are as responsive to IL-16 as their CD4 wild-type equivalents in both assays testing for IL-16 function (chemotaxis and production of proinflammatory cytokines). In addition, the inhibitory effect of soluble CD4 on IL-16 function observed using CD4 wild type murine cells was not observed using CD4 knockout cells. These data demonstrate that CD4 is not required for IL-16 function and suggest that another molecule acts as the major receptor.

Molecular cloning and sequence analysis of interleukin 16 from nonhuman primates and from the mouse.

Abstract Interleukin 16 (IL-16) is synthesized as a 67 000 Mr precursor (pro-IL-16), but only a carboxy terminal part of 12 000–14 000 Mr is secreted by CD8(+) lymphocytes. This lymphokine binds to CD4 and has been shown to induce migration, affect the activation state of T cells, and inhibit immunodeficiency virus replication. It has been suggested that CD8(+) cell-derived soluble factors play a pivotal role in protecting natural-host nonhuman primates from developing immunodeficiency following SIV infection. In a first attempt to address this question, we cloned and sequenced the IL-16 cDNA from different primates. Here we report the pro-IL-16 sequence from chimpanzees, African green monkeys (AGM), rhesus macaques, and cynomolgus macaques. In order to compare and analyze structural motifs possibly involved in processing, intracellular targeting, or secretion, we extended our study to the New World monkeys saimiri and aotus and to the mouse. Alignments of deduced amino acids reveal that the human protein shares 99% similarity to that of chimpanzees, approximately 95% to rhesus, cynomolgus and AGM, about 90% to aotus and saimiri, and 77.5% to the mouse. Phylogenetic analyses revealed the expected evolutionary groupings.

Chemoattractant Factors and the Control of Human Immunodeficiency Virus Replication

Factors secreted by CD8(+) T cells have been described to suppress immunodeficiency virus replication. The research efforts to identify these factors led to the proposal of some candidate proteins as being responsible for the antiviral effects. Chemokines and IL-16 are secreted by CD8(+) T cells and inhibit HIV replication through different mechanisms. However, their antiviral properties cannot fully explain the inhibitory activities found in cell culture supernatants from CD8(+) T cells.