HIV-1 induces phenotypic and functional perturbations of B cells in chronically infected individuals

A number of perturbations of B cells has been described in the setting of HIV infection; however, most remain poorly understood. To directly address the effect of HIV replication on B cell function, we investigated the capacity of B cells isolated from HIV-infected patients to respond to a variety of stimuli before and after reduction of viremia by effective antiretroviral therapy. B cells taken from patients with high levels of plasma viremia were defective in their proliferative responses to various stimuli. Viremia was also associated with the appearance of a subpopulation of B cells that expressed reduced levels of CD21. After fractionation into CD21(high)- and CD21(low)-expressing B cells, the CD21(low) fraction showed dramatically reduced proliferation in response to B cell stimuli and enhanced secretion of immunoglobulins when compared with the CD21(high) fraction. Electron microscopic analysis of each fraction revealed cells with plasmacytoid features in the CD21(low) B cell population but not in the CD21(high) fraction. These results indicate that HIV viremia induces the appearance of a subset of B cells whose function is impaired and which may be responsible for the hypergammaglobulinemia associated with HIV disease.

Unequal VH gene rearrangement frequency within the large VH7183 gene family is not due to recombination signal sequence variation, and mapping of the genes shows a bias of rearrangement based on chromosomal location

Much of the nonrandom usage of V, D, and J genes in the Ab repertoire is due to different frequencies with which gene segments undergo V(D)J rearrangement. The recombination signal sequences flanking each segment are seldom identical with consensus sequences, and this natural variation in recombination signal sequence (RSS) accounts for some differences in rearrangement frequencies in vivo. Here, we have sequenced the RSS of 19 individual V(H)7183 genes, revealing that the majority have one of two closely related RSS. One group has a consensus heptamer, and the other has a nonconsensus heptamer. In vitro recombination substrate studies show that the RSS with the nonconsensus heptamer, which include the frequently rearranging 81X, rearrange less well than the RSS with the consensus heptamer. Although 81X differs from the other 7183-I genes at three positions in the spacer, this does not significantly increase its recombination potency in vitro. The rearrangement frequency of all members of the family was determined in microMT mice, and there was no correlation between the in vitro recombination potential and V(H) gene rearrangement frequency in vivo. Furthermore, genes with identical RSS rearrange at different frequencies in vivo. This demonstrates that other factors can override differences in RSS potency in vivo. We have also determined the gene order of all V(H)7183 genes in a bacterial artificial chromosome contig and show that most of the frequently rearranging genes are in the 3' half of the region. This suggests that chromosomal location plays an important role in nonrandom rearrangement of the V(H)7183 genes.

B-cell repertoire formation: role of the recombination signal sequence in non-random V segment utilization

V, D, and J gene segments rearrange at different frequencies in vivo. Each rearranging gene segment is flanked by a recombination signal sequence (RSS), which is composed of a conserved heptamer and nonamer, separated by a spacer of conserved length but not conserved sequence. We summarize data from our lab and other labs showing that in many cases, but not all, the RSS can account for differences in recombination frequencies observed in vivo. Our approach is to determine the initial frequency of rearrangement of the V genes in vivo, and then place the RSSs of two V genes into a competition recombination substrate to determine the relative frequency with which the two RSSs support recombination. In one example, we have shown that a polymorphism in the heptamer of a Vkappa gene can result in a significant reduction in recombination frequency. This particular allele is prevalent in Navajos and absent in other populations. We suggest that this single change may play a major role in the high susceptibility of Navajos to Haemophilus influenzae infection, since this Vkappa gene is important in the antibody response to this bacteria. We also describe experiments showing that the sequence of the spacer of the RSS can play an important role in relative recombination frequencies.