Inherited resistance to HIV-1 conferred by an inactivating mutation in CC chemokine receptor 5: studies in populations with contrasting clinical phenotypes, defined racial background, and quantified risk

BACKGROUND

CC chemokine receptor 5 (CCR5) is a cell entry cofactor for macrophage-tropic isolates of human immunodeficiency virus-1 (HIV-1). Recently, an inactive CCR5 allele (designated here as CCR5-2) was identified that confers resistance to HIV-1 infection in homozygotes and slows the rate of progression to AIDS in heterozygotes. The reports conflict on the effect of heterozygous CCR5-2 on HIV-1 susceptibility, and race and risk levels have not yet been fully analyzed. Here we report our independent identification of CCR5-2 and test its effects on HIV-1 pathogenesis in individuals with contrasting clinical outcomes, defined race, and quantified risk.

MATERIALS AND METHODS

Mutant CCR5 alleles were sought by directed heteroduplex analysis of genomic DNA from random blood donors. Genotypic frequencies were then determined in (1) random blood donors from North America, Asia, and Africa; (2) HIV-1+ individuals; and (3) highly exposed-seronegative homosexuals with quantified risk.

RESULTS

CCR5-2 was the only mutant allele found. It was common in Caucasians, less common in other North American racial groups, and not detected in West Africans or Tamil Indians. Homozygous CCR5-2 frequencies differed reciprocally in highly exposed-seronegative (4.5%, n = 111) and HIV-1-seropositive (0%, n = 614) Caucasians relative to Caucasian random blood donors (0.8%, n = 387). This difference was highly significant (p < 0.0001). By contrast, heterozygous CCR5-2 frequencies did not differ significantly in the same three groups (21.6, 22.6, and 21.7%, respectively). A 55% increase in the frequency of heterozygous CCR5-2 was observed in both of two cohorts of Caucasian homosexual male, long-term nonprogressors compared with other HIV-1+ Caucasian homosexuals (p = 0.006) and compared with Caucasian random blood donors. Moreover, Kaplan-Meier estimates indicated that CCR5-2 heterozygous seroconvertors had a 52.6% lower risk of developing AIDS than homozygous wild-type seroconvertors.

CONCLUSIONS

The data suggest that homozygous CCR5-2 is an HIV-1 resistance factor in Caucasians with complete penetrance, and that heterozygous CCR5-2 slows the rate of disease progression in infected Caucasian homosexuals. Since the majority (approximately 96%) of highly exposed-seronegative individuals tested are not homozygous for CCR5-2, other resistance factors must exist. Since CCR5-2 homozygotes have no obvious clinical problems, CCR5 may be a good target for the development of novel antiretroviral therapy.

In utero exposure to Onchocerca volvulus: relationship to subsequent infection intensity and cellular immune responsiveness

Afro-Ecuadorian individuals from an area where Onchocerca volvulus is hyperendemic have been monitored for infection over the past 16 years. To determine whether in utero exposure to O. volvulus biases a child's subsequent immune responses, children (9 to 16 years old) for whom the mother's infection status was known were chosen for study. Children of infected mothers (n = 19) had significantly higher levels of skin microfilariae than children of uninfected mothers (n = 13; P = 0.021). While the serum levels of O. volvulus-specific immunoglobulin G (IgG), IgG subclasses, and IgE showed no significant differences between the two groups of children, peripheral blood mononuclear cells of children of infected mothers produced higher levels of Th2-type cytokines to several parasite antigens and lower levels of Th1-type cytokines to nonparasite antigens than those of children of uninfected mothers. Thus, in utero exposure to O. volvulus has a long-term effect on the child's subsequent cellular immune response that may render the child more susceptible to O. volvulus infection postnatally.

RANTES in onchocerciasis: changes with ivermectin treatment

Adverse reactions are seen relatively frequently after treatment of onchocerciasis patients with ivermectin. The chemokines RANTES and IL-8, which have both chemotactic and activation properties for eosinophils and neutrophils, respectively, may have a role in the pathogenesis of post-treatment reactions. Circulating levels of the chemokines and the cytokines tumour necrosis factor-alpha (TNF-alpha) and IL-6 were measured in the plasma of 22 Onchocerca volvulus-infected subjects. Peaks of mean circulating levels of RANTES and TNF-alpha were seen at 6 h after ivermectin administration. Peripheral eosinophil counts declined at 36 h post-treatment and an early peak in RANTES levels was associated with a delay in peripheral eosinopenia. RANTES levels were negatively correlated with severity of rash (P < 0.001) and lymphoedema (P < 0.05), suggesting that high circulating levels of RANTES may inhibit eosinophil sequestration. No changes in circulating levels of IL-8 were seen. These findings suggest a possible role of circulating RANTES in modulating eosinophil sequestration in vivo.

Differential regulation of antigen-specific IgG4 and IgE antibodies in response to recombinant filarial proteins

Having identified two recombinant filarial proteins (Ov27 and OvD5B) that induced patient peripheral blood mononuclear cells to produce antigen-specific IgG4/IgE antibodies in vitro, we assessed the role these filarial antigens play in inducing antigen-specific isotype switching (gamma 4 and epsilon) in the absence of T cells. Purified CD19+ s gamma-/s epsilon- B cells were cultured with either of these antigens in the presence of anti-CD40 mAb and human IL-4. Both antigen and polyclonal signals delivered by IL-4 (or IL-13) were necessary for the induction of specific IgG4/IgE antibodies. To assess the role played by cytokines produced by B lymphocytes in antigen-driven selection of the gamma 4 or epsilon isotype, neutralizing anti-cytokine antibodies were used in vitro. While anti-IL-12 antibodies did not alter the antigen-specific IgG4/IgE production, anti-IL-6, anti-IL-13 and anti-tumor necrosis factor-alpha antibodies significantly inhibited the production of IgG4/IgE. Anti-IL-2 and anti-IL-10 antibodies appeared to down-regulate antigen-specific IgG4 antibodies without affecting antigen-specific IgE antibodies. Although anti-CD21 antibodies had no effect on specific IgE antibodies, they up-regulated specific IgG4 antibodies, a finding paralleled by anti-CD23 antibodies. These data suggest that certain filarial antigen-specific IgG4/IgE responses can be differentially regulated and that certain endogenously produced molecules from B cells-such as IL-2, IL-10, CD23 and CD21-play a significant role in the induction of specific isotypes of antigen-specific antibodies.

A major allergen of lymphatic filarial nematodes is a parasite homolog of the gamma-glutamyl transpeptidase

BACKGROUND

Bm2325, a major IgE-inducing antigen of the filarial parasite Brugia malayi has been implicated in the pathology of tropical pulmonary eosinophilia (TPE), a pulmonary syndrome thought to result from hypersensitivity to microfilariae.

MATERIALS AND METHODS

Affinity-purified IgE to Bm2325 from patients with TPE was used to identify a complementary DNA (cDNA) from a B. malayi expression library. Sequence analysis of the cDNA revealed a hitherto unknown parasite protein. Immunoblotting of the recombinant filarial protein using sera of patients with TPE determined its IgE-binding capacity. Reactivity to human lung epithelial cell proteins was analyzed using murine anti-Bm2325 antibodies and serum from patients with TPE.

RESULTS

The predicted protein is a homolog of the entire precursor of the gamma-glutamyl transpeptidase (gamma-GT), a key enzyme in the synthesis and degradation of glutathione. The filarial precursor encodes both the heavy (H) and the light (L) chain subunits and shares structural similarities with the mammalian enzymes. The Bm2325 allergen was identified as the homolog of the enzyme light chain subunit. Murine antibodies against the recombinant parasite gamma-GT cross-reacted with the human enzyme present in human airway epithelial cells, and human gamma-GT is a target of antibodies present in the serum of patients with TPE.

CONCLUSION

Molecular mimicry between the parasite gamma-GT homolog and the host membrane-bound gamma-GT present in lung epithelial cells likely contributes to the pathogenesis observed in tropical pulmonary eosinophilia.

Stage-specific induction of cytokines regulates the immune response in lymphatic filariasis

Parasite stage-specific T cell responses were studied in Indians with lymphatic filariasis manifesting as elephantiasis (CP, n = 11) and asymptomatic microfilaremia (MF, n = 8), using antigens derived from the microfilarial, adult male only, and mixed adult male and female worms. Proliferative responses to microfilarial and mixed (male-female adult worm) antigens in MF individuals were markedly impaired compared to corresponding responses in individuals with CP. In contrast, T cell proliferative responses to adult male-derived antigens were not statistically different between the two groups. Analysis of antigen-driven cytokine secretion by peripheral blood mononuclear cells from MF and CP individuals revealed significantly lower IL-2 and IFN-gamma production by MF in response to microfilarial and mixed antigens (but not to adult male antigen) compared to CP individuals. No differences were observed between MF and CP in parasite antigen-driven IL-4 or IL-5 production. Spontaneous and parasite-specific IL-10 secretion was also measured to determine if cytokine cross-regulation of Th1 responses may be a mechanism underlying the observed Th1 suppression. Spontaneous and microfilarial antigen-driven IL-10 was found to be significantly higher in MF than in CP individuals. These data indicate that MF individuals exhibit preferentially impaired Th1-type responses to microfilarial antigens and that microfilarial-induced IL-10 may be critical in the downregulation of specific Th1 responses.

Diethylcarbamazine-induced reversal of early lymphatic dysfunction in a patient with bancroftian filariasis: assessment with use of lymphoscintigraphy

Exposure of expatriates to the infective larvae of Wuchereria bancrofti can result in the early development of signs of lymphatic obstruction. The findings on the clinical presentation of expatriates are distinct from the chronic pathological findings seen among the native population and are similar to the findings in experimentally infected persons. We report the case of a Peace Corps volunteer who developed acute lymphatic dysfunction within 3 months of arriving in an area that was endemic for filariasis. The diagnosis was established clinically and by demonstrating the presence of antibodies to recombinant proteins specific for patients with lymphatic filariasis. Lymphatic flow was markedly abnormal when assessed with use of 99mTc-lymphoscintigraphy. Treatment with diethylcarbamazine reversed both the physical and lymphoscintigraphic abnormalities.

Identification of surface molecules associated with physiologic activation of eosinophils. Application of whole-blood flow cytometry to eosinophils

Activation is central to the eosinophil's functional role as an immune responder cell. To evaluate such activation in cells freshly isolated from peripheral blood, a method for whole-blood immunostaining and flow cytometry-based eosinophil selection was developed. Simultaneous comparison of purified eosinophils and whole-blood cells revealed significant differences in the levels of expression of various surface molecules, which suggested that the purification process activated the eosinophils. Subsequent analyses were conducted with the whole-blood assay. When eosinophils from helminth-infected persons (n = 18) were compared with those from normal individuals (n = 10), the early activation marker CD69 was found to be significantly increased (geometric mean (GM) = 4.3 vs. 1.0%, p = 0.04). The granulocyte activation marker CD66 was also up-regulated on eosinphils from helminth patients (GM = 53.3 vs. 31.0%, p = 0.044), as was the tetraspan family molecule CD81 (TAPA-1; GM = 79.4 vs. 48.2%, p = 0.02). Conversely, in vivo CD23 (FcepsilonRII) expression on eosinophils was decreased in the presence of parasitic infection (GM = 0.9 vs. 5.7%, p = 0.02). Expression of the eosinophil surface molecules CD69, CD81, and CD23 was significantly enhanced after cytokine stimulation in vitro with IL-3 or GM-CSF. In vivo, specific anthelmintic therapy resulted in decreased CD66 and CD25 expression (p < 0.05 compared with pretreatment) to levels approaching those seen in uninfected normal individuals. These findings indicate the dynamic nature of eosinophil surface molecules and demonstrate an important role for whole-blood staining in developing an understanding of the nature of eosinophil activation and of their role in inflammatory reactions to helminth parasites.

Identification of surface molecules associated with physiologic activation of eosinophils. Application of whole-blood flow cytometry to eosinophils

Activation is central to the eosinophil's functional role as an immune responder cell. To evaluate such activation in cells freshly isolated from peripheral blood, a method for whole-blood immunostaining and flow cytometry-based eosinophil selection was developed. Simultaneous comparison of purified eosinophils and whole-blood cells revealed significant differences in the levels of expression of various surface molecules, which suggested that the purification process activated the eosinophils. Subsequent analyses were conducted with the whole-blood assay. When eosinophils from helminth-infected persons (n = 18) were compared with those from normal individuals (n = 10), the early activation marker CD69 was found to be significantly increased (geometric mean (GM) = 4.3 vs. 1.0%, p = 0.04). The granulocyte activation marker CD66 was also up-regulated on eosinphils from helminth patients (GM = 53.3 vs. 31.0%, p = 0.044), as was the tetraspan family molecule CD81 (TAPA-1; GM = 79.4 vs. 48.2%, p = 0.02). Conversely, in vivo CD23 (FcepsilonRII) expression on eosinophils was decreased in the presence of parasitic infection (GM = 0.9 vs. 5.7%, p = 0.02). Expression of the eosinophil surface molecules CD69, CD81, and CD23 was significantly enhanced after cytokine stimulation in vitro with IL-3 or GM-CSF. In vivo, specific anthelmintic therapy resulted in decreased CD66 and CD25 expression (p &lt; 0.05 compared with pretreatment) to levels approaching those seen in uninfected normal individuals. These findings indicate the dynamic nature of eosinophil surface molecules and demonstrate an important role for whole-blood staining in developing an understanding of the nature of eosinophil activation and of their role in inflammatory reactions to helminth parasites.

Evaluation of a polymerase chain reaction-based assay for diagnosis of Wuchereria bancrofti infection

To assess the utility of a polymerase chain reaction (PCR)-based method for diagnosis of Wuchereria bancrofti infection, blood, plasma, and paraffin-embedded tissue samples were tested using a PCR-based assay that detects a W. bancrofti-specific repetitive DNA sequence. The assay was positive in 100 microL of blood from 40 of 42 microfilaria-positive subjects, the 2 subjects with negative assays having microfilarial counts of 1. Samples from 127 uninfected subjects were PCR-negative. The assay was also positive in 7 of 10 daytime samples in regions where infection is nocturnally periodic; PCR amplification from paraffin-embedded sections established the diagnosis of W. bancrofti infection in another 2 cases. A microtiter ELISA plate-based method was developed for rapid evaluation of large numbers of samples. These results suggest that this PCR-based assay will be useful in diagnosis of W. bancrofti infection in a variety of clinical settings.

Elevations in granulocyte-macrophage colony-stimulating factor and interleukin-5 levels precede posttreatment eosinophilia in onchocerciasis

The eosinophil survival assay was used to quantitate cytokines in 17 serial serum samples from 10 patients treated for onchocerciasis with diethylcarbamazine. Eosinophils isolated from normal donors were cultured for 4 days in the presence of patients' sera, and cell viability was determined. Serum specimens from 9 of 10 patients enhanced eosinophil survival from 4.8% +/- 2.2% (mean +/- SE) before treatment to 50.0% +/- 6.4% after treatment. Survival enhancement activity peaked before posttreatment eosinophilia. Antibodies to interleukin (IL)-5, granulocyte-macrophage colony-stimulating factor (GM-CSF), and IL-3 were used to block cytokine activity in 22 serum samples. Antibodies to IL-5 blocked survival in 5 samples, antibodies to GM-CSF blocked survival in 6 samples, and a combination of antibodies to IL-5 and GM-CSF blocked survival in 8 additional samples. Overall, posttreatment sera from patients treated for onchocerciasis enhanced eosinophil survival; both GM-CSF and IL-5 may promote the posttreatment eosinophilia in filarial infection.

A polymerase chain reaction assay for detection of the parasite Wuchereria bancrofti in human blood samples

To identify Wuchereria bancrofti DNA sequences that could be used as the basis for a simple and rapid parasite detection assay, a genomic library of W. bancrofti was constructed and screened for highly repeated DNA. The repeat found with the highest copy number was 195 basepairs (bps) long, 77% AT, and 300 copies per haploid genome. This sequence was designated the Ssp I repeat because it has a unique recognition site for that restriction endonuclease in all or most of the repeat copies. The Ssp I repeat DNA family is dispersed, genus-specific, and exists in all of the different geographic isolates of W. bancrofti tested. Based on DNA sequence analysis of this repeat, we have developed an assay to detect very small quantities of W. bancrofti DNA using the polymerase chain reaction (PCR). With this PCR assay, the Ssp I repeat was detected in as little as 1 pg of w. bancrofti genomic DNA (about 1% of the DNA in one microfilaria) added to 100 microliters of human blood. The PCR assay also amplified Ssp I repeat DNA from geographic isolates of W. bancrofti from around the world but not from other species of filariae or from human or mosquito DNA. Microfilaria-positive human blood samples collected in Mauke, Cook Islands were shown to be Ssp I PCR-positive, while microfilaria-negative samples were PCR-negative. The specificity and sensitivity of the Ssp I PCR assay indicates that this approach has significant potential for improved screening of large human populations for active W. bancrofti infection.

High levels of spontaneous and parasite antigen-driven interleukin-10 production are associated with antigen-specific hyporesponsiveness in human lymphatic filariasis

To determine whether counterregulation by interleukin (IL)-10 plays a role in the generation or maintenance of the antigen-specific hyporesponsiveness seen in asymptomatic microfilaremic (MF) patients, parasite antigen (PAg)- and nonparasite antigen (NPAg)-driven IL-10 production by peripheral blood mononuclear cells (PBMC) was studied in 10 MF patients and in ll patients with chronic lymphatic pathology (CP). PBMC from MF patients spontaneously secreted 10-fold more IL-10 than did PBMC from patients with CP. PAg also induced significantly more IL-10 production by PBMC from CP patients. There was a negative correlation between PAg driven IL-10 production by PBMC and PAg-specific T cell proliferation in the MF group. IL-10 secretion by plastic adherent cells from MF persons was higher in response to PAg than NPAg, whereas IL-6 and tumor necrosis factor-alpha secretion were equivalent for PAg and NPAg, suggesting that PAg preferentially induces IL-10 secretion in these cells. Thus, PAg-induced IL-10 likely plays an important role in down-regulating antigen-specific proliferative responses in MF patients.

Polymerase chain reaction-based assessment after macrofilaricidal therapy in Onchocerca volvulus infection

A recently developed polymerase chain reaction (PCR)-based assay is significantly more sensitive than current methods for diagnosing Onchocerca volvulus infection, and it overcomes many difficulties in identifying active onchocerciasis. Since chemotherapy is widely used to treat onchocerciasis, the utility of PCR in assessing responses to treatment and in predicting recrudescence is important. Twenty-eight patients who had skin snips positive for microfilariae (Mf) were studied 120 days after receiving amocarzine, when each was negative for Mf: 16 (57%) were positive for O. volvulus DNA in the PCR-based assay. Of these, 14 (88%) were Mf positive when reassessed parasitologically on day 240, and all were Mf positive on day 365. Equally important was the finding that 12 patients had cleared both Mf and Mf DNA; only 1 was Mf positive at day 240. This suggest that the PCR-based assay provides a sensitive means assessing infection status after macrofilaricidal chemotherapy and is an early predictor of persons likely to have a recurrence of Mf.

Immunoglobulin G subclass responses of children during infection with Onchocerca volvulus

To characterize the patterns of immunoglobulin G (IgG) subclass and IgE reactivity during the early stages of onchocerciasis, sera were collected from 224 children (age groups, 2 to 5, 6 to 10, and 11 to 15 years) residing in a region of Sierra Leone where Onchocerca volvulus is endemic, and these samples were tested by enzyme-linked immunosorbent assay for their reactivity to adult antigens (OvAg) and against four recombinant proteins (OV11, OV27, OV29, and OV16). Over 88% of the samples contained detectable levels of anti-OvAg IgG. In samples from microfilaria (MF)-positive children, IgG4 responses were significantly elevated and constituted on average 39, 35 and 28% of the total IgG responses for the age groups of 2 to 5, 6 to 10, and 11 to 15 years, respectively. For MF-negative individuals, the mean contributions of IgG4 to the total IgG response were 11% (2 to 5 years), 27% (6 to 10 years), and 56% (11 to 15 years). OvAg-specific IgE was detectable in the sera from both MF-negative and MF-positive individuals. To increase the specificity of the response, recombinant antigens OV11, OV27, and OV29 were tested individually or as a cocktail. Nearly 50% of the MF-negative children and 85% of the MF-positive children had detectable levels of IgG against at least one of the recombinant antigens. Only a small portion of the IgG against the recombinant peptides was IgG4. The prevalence of IgG against OV16 in samples from MF-negative children was 51%, and that for MF-positive children was 75%. The general profile of the humoral immune responses mounted by both MF-positive and a large percentage of the MF-negative children during the initial phases of infection with O. volvulus is similar to the profile reported for adults harboring chronic O. volvulus infections. These results suggest that very quickly after infection, the interactions between parasite and host result in an immunological environment that may contribute to the maintenance of a long-term, chronic infection.

Technical report. Optimizing probe selection in directed heteroduplex analysis using HDprobe 1.1

Directed heteroduplex analysis (DHDA) has proven to be a powerful technique for rapid geotyping in human populations. This strategy should also have widespread utility in differentiating closely related organisms of medical and public health importance through identification of DNA sequence polymorphisms. Identifying an optimal probe sequence for use in DHDA has required empirical testing of both the positive and negative strands of a number of potential probes. To identify optimal probes more efficiently, a computer program has been developed that predicts the number of potential stable and unstable mismatches between a probe and its target sequences in DHDA. This information can then be used to predict--from among a group of potential probes--which one will be the most successful in differentiating closely related homologues of a targeted gene sequence. This approach was tested on a number of probe and target sequences derived from the mitochondrial NADH dehydrogenase subunit 4 gene of the West African black fly, Simulium damnosum sensu lato. The number of unstable mismatches predicted to occur in a given heteroduplex by the computer program was found to be important in differentiating closely related species. Therefore, this strategy is useful in identifying informative probes in the development of new DHDA-based assays.

Immunoglobulin kappa chain allotypes (KM) in onchocerciasis

GM and KM allotypes, powerful tools for genetic characterization of human populations, have been shown to play an important role in genetic predisposition to some infectious diseases. Two diverse racial groups--Afro-Ecuadorians and Amerindians--living in a single restricted geographical area of Ecuador, appear to have different risk factors for acquisition and clinical expression of onchocerciasis, a disease caused by the filarial parasite Onchocerca volvulus. In this study, GM and KM allotypes were determined in 25 Afro-Ecuadorians and 24 Amerindians infected with Onchocerca volvulus (INF) and in putative immune individuals (PI). In Afro-Ecuadorians, the frequency of the homozygous KM 3 phenotype was significantly decreased in INF as compared with the PI group (20 vs. 68%; P= 0.0012), while the frequency of the heterozygous KM 1,3 phenotype was increased in INF as compared with the PI subjects (48 vs. 9%; P= 0.0044). These results suggest that in Afro-Ecuadorians KM 3 is associated with a lower relative risk (resistance), whereas KM 1,3 is associated with an increased risk (susceptibility) of onchocerciasis.

Resistance to Onchocerca volvulus: differential cellular and humoral responses to a recombinant antigen, OvMBP20/11

Persons putatively immune (PI) to Onchocerca volvulus (Ov) infection were identified in Ecuador on the basis of epidemiologic, clinical, and parasitologic findings. Immune responses of PI subjects to a recombinant onchocercal protein, OvMBP20/11, were determined and compared with those of a comparable infected (INF) group from the same Ov-endemic area. PI subjects had significantly less antibody reactivity to this molecule; however, not all INF subjects had an antibody response. IgG1 and IgG4 were the predominant IgG subclasses induced to this molecule, and the amount of IgG1 produced was the only significant difference between the PI and INF groups. In contrast to the antibody responses, proliferative responses to OvMBP20/11 were significantly higher in PI than in INF subjects. Cytokine analysis of peripheral blood mononuclear cell culture supernatants revealed that INF subjects produced significantly more interleukin-10 in response to OvMBP20/11 than did PI subjects. This antigen induced few other cytokines, and there were no differences between study groups.

Differential regulation of alternative 3' splicing of epsilon messenger RNA variants

Alternative 3' splicing of the one active human epsilon heavy chain gene results in variants of epsilon mRNA encoding distinct IgE proteins. The same relative amounts of these epsilon mRNA variants were produced by non-atopic donor B cells when driven in a variety of T-dependent or T-independent systems. The most abundant variants were those for classic secreted epsilon a novel secreted form (CH4-M2"). In contrast, cells from subjects with high levels of serum IgE secondary to parasitic infection or atopy spontaneously produced higher relative levels of the CH4-M2' epsilon mRNA variant, lower relative amounts of both the membrane and CH4-M2" secreted variants, and very low levels of the CH4'-CH5 variant. The existence of and corresponding changes in levels of the CH4-M2'-encoded secreted protein were demonstrated. IL-10 induced this same differential expression of epsilon splice variants in vitro when used to costimulate IL-4 plus CD40-driven B cells and could differentially enhance the production of CH4-M2' protein by established IgE-secreting cell lines. Inhibition of IgE by cross-linking the low affinity IgE receptor (CD23) decreased the levels of epsilon mRNA and resulted in a distinct pattern of epsilon mRNA characterized by a dramatic decrease in CH4-M2' splice variant. IL-6, IL-2, or IFN-gamma did not change the epsilon mRNA pattern. Overall, the absolute and relative amounts of the different epsilon mRNA splice variants produced appear to be controlled in a differentiation-related fashion.

Differential regulation of alternative 3' splicing of epsilon messenger RNA variants

Alternative 3' splicing of the one active human epsilon heavy chain gene results in variants of epsilon mRNA encoding distinct IgE proteins. The same relative amounts of these epsilon mRNA variants were produced by non-atopic donor B cells when driven in a variety of T-dependent or T-independent systems. The most abundant variants were those for classic secreted epsilon a novel secreted form (CH4-M2"). In contrast, cells from subjects with high levels of serum IgE secondary to parasitic infection or atopy spontaneously produced higher relative levels of the CH4-M2' epsilon mRNA variant, lower relative amounts of both the membrane and CH4-M2" secreted variants, and very low levels of the CH4'-CH5 variant. The existence of and corresponding changes in levels of the CH4-M2'-encoded secreted protein were demonstrated. IL-10 induced this same differential expression of epsilon splice variants in vitro when used to costimulate IL-4 plus CD40-driven B cells and could differentially enhance the production of CH4-M2' protein by established IgE-secreting cell lines. Inhibition of IgE by cross-linking the low affinity IgE receptor (CD23) decreased the levels of epsilon mRNA and resulted in a distinct pattern of epsilon mRNA characterized by a dramatic decrease in CH4-M2' splice variant. IL-6, IL-2, or IFN-gamma did not change the epsilon mRNA pattern. Overall, the absolute and relative amounts of the different epsilon mRNA splice variants produced appear to be controlled in a differentiation-related fashion.