Human immunodeficiency virus type 1 can generally use CCR3 and CCR5 for cell entry. We show that envelopes with novel phenotypes arise during "coreceptor switch": one loses the ability to use CCR3 (R5-only phenotype), and another gains use of CXCR4 in addition to CCR5 and CCR3 (R3/R5/X4-using phenotype). The envelope determinants for CCR3 use mapped to three amino acids. One, N356 in conserved region 3, is a potential glycosylation site and has not previously been associated with coreceptor use. The other two, R440 and N448 in conserved region 4, are proximal to but distinct from residues already identified as being important for CCR5 binding.We have previously described that efficient CCR3 use is a general feature of human immunodeficiency virus type 1 (HIV-1) envelopes (Envs) from uncultured viruses (1). Most Envs from patient blood could use CCR3 as well as CCR5 (R3/R5). Potential targets for CCR3-mediated infection include microglial cells, macrophages, eosinophils, and T-helper 2 cells. Here the dynamics of coreceptor use, from acute infection to disease progression, was tested with one patient. Figure 1 shows a sharp decline in CD4 cell numbers and an elevation in viral load between days 608 and 957. Since this is characteristic of R5/X4 "coreceptor switch," we determined coreceptor use by the prevailing quasispecies. Envs were cloned by reverse transcription-PCR and inserted into a replication-competent HIV-1 vector, and viruses were produced by transfection of 293T cells (1, 2). Coreceptor use on NP2/ CD4 and U87/CD4 cells expressing various receptors was determined. Infection (focus-forming units [FFU])/ml) was detected by p24 immunostaining after 48 h of culture (1). As expected, Envs from acute (day 12 to 32) and asymptomatic (day 608) infection were R3/R5-tropic. Indeed, the efficiency of CCR3 use was similar to that of CCR5 use in the majority of Envs (Table 1). We have previously shown that the high level of CCR3 use observed is not an artifact of our system (1). Little or no use of CCR1, CCR2b, CCR8, and APJ was seen (data not shown). Envs isolated from day 957 revealed two different receptor phenotypes (Table 1). Both types of Env maintained CCR5 use, but two lost the use of CCR3 (8.9.I and 8.9.K). The other maintained CCR3 use but additionally gained CXCR4 use (8.9.B, 8.9.D, 8.9.H, and 8.9.J). Gain of CXCR4 use with time occurs in about 50% of HIV-1 patients, but as far as we are aware, the phenotypic switch (from R3/R5 to R5 only or to R3/R5/X4) described here has not been previously reported (5, 13, 14).The isolation of closely related Envs with different coreceptor preferences allowed us to map Env determinates of CCR3 use. Env fragments were swapped between 8.9.K (R5 only) and 8.8.3 (R3/R5). Figure 2A shows the amino acid alignment of these Envs and the prototypic R3/R5 Env YU2. Regions were swapped using conserved BglII and PpuMI restriction sites in combination with BstEII and MluI sites, which were incorporated in the primers used for Env cloning ( Fig. 2A). Figure 3A shows the chimeric E...

Crohn's disease and ulcerative colitis are idiopathic chronic inflammatory diseases that primarily affect the gastrointestinal tract. The underlying causes remain poorly understood, but there is a growing body of evidence advocating a likely primary pathogenic role for immunodeficiency in the development of Crohn's lesions. Concordantly, a number of congenital immunodeficiencies disrupting the cellular innate immune system strongly predispose to noninfectious, Crohn's-like inflammatory bowel disease. There are case reports and series suggesting that the same may be true for some of the congenital adaptive and complement immunodeficiencies. This review considers and critiques these potential associations.