Temporal Variation of the Merozoite Surface Protein-2 Gene of Plasmodium falciparum

Extensive polymorphism of key parasite antigens is likely to hamper the effectiveness of subunit vaccines against Plasmodium falciparum infection. However, little is known about the extent of the antigenic repertoire of naturally circulating strains in different areas where malaria is endemic. To address this question, we conducted a study in which blood samples were collected from parasitemic individuals living within a small hamlet in Western Irian Jaya and subjected to PCR amplification using primers that would allow amplification of the gene encoding merozoite surface protein-2 (MSP2). We determined the nucleotide sequence of the amplified product and compared the deduced amino acid sequences to sequences obtained from samples collected in the same hamlet 29 months previously. MSP2 genes belonging to both major allelic families were observed at both time points. In the case of the FC27 MSP2 family, we observed that the majority of individuals were infected by parasites expressing the same form of MSP2. Infections with parasites expressing 3D7 MSP2 family alleles were more heterogeneous. No MSP2 alleles observed at the earlier time point were detectable at the later time point, either for the population as a whole or for individuals who were assayed at both time points. We examined a subset of the infected patients by using blood samples taken between the two major surveys. In no patients could we detect reinfection by a parasite expressing a previously encountered form of MSP2. Our results are consistent with the possibility that infection induces a form of strain-specific immune response against the MSP2 antigen that biases against reinfection by parasites bearing identical forms of MSP2.The development of a host-protective immune response against Plasmodium falciparum takes several years and many episodes of infection, at least for children living in areas where malaria is endemic. One of the reasons for this is believed to be the large number of distinct parasite strains circulating within an area of endemicity and the assumption that exposure must occur to a sufficiently large sample of these before lasting immunity is induced. However, the detailed epidemiology of endemic malaria infection remains poorly understood at the molecular level, and there is surprisingly little nucleotide sequence data to support the concept of a large repertoire of antigenically distinct strains.There are at least six antigenically diverse proteins of the asexual stage that are known to be the target of potentially protective host responses. The definition of antigenically distinct strains involves identification of the allelic form expressed at all antigenically diverse loci—the extended antigenic haplotype. The loci would include merozoite surface protein-1 to -3 (3), apical membrane antigen-1 (17), S-antigen (6), and P. falciparum erythrocyte membrane protein-1 (PfEMP-1) (5). Such a complete molecular definition of infecting parasites is a highly ambitious task, particularly in the case of blood samples collected from patients harboring mixed infections. Accordingly, most studies focus on one or other of the antigenically diverse antigens. We have elected to study merozoite surface protein-2 (MSP2) (27), a 45- to 50-kDa glycoprotein anchored in the merozoite surface by a glycosylphosphatidylinositol anchor. This surface protein is a promising candidate for inclusion in a malaria subunit vaccine, as both in vitro and in vivo studies have demonstrated the ability of immune responses to MSP2 to inhibit parasite multiplication (23, 25). However, the efficacy of any subunit vaccine containing a single form of MSP2 may be limited by the presence of antigenically distinct parasite strains within an area of endemicity. We will adopt the recently proposed convention for parasite genes and gene products of denoting the gene sequence as MSP2 and the protein as MSP2.Sequence polymorphism has been described for MSP2 genes of both laboratory-maintained isolates (29) and field isolates (14, 16, 19, 30). Comparison of MSP2 gene sequences from these isolates reveals highly conserved 5′ and 3′ sequences that flank a central variable region. This central region is composed of repeats flanked by nonrepetitive sequences. The nonrepetitive sequences are one or other of two distinct forms that define two allelic families, FC27 and IC-1/3D7 (29). The central repeats are more variable and define the individual alleles of MSP2. There is a correlation between the general form of the central repeat sequence and the allelic family. For example, FC27 family members have variants of a central 96-bp pair sequence that may be present in one to four copies followed by a 21-bp partial repeat and a variably represented 36-bp sequence that may be present in one to five copies. In contrast, alleles belonging to the 3D7 family show a central repeat region made up of variable numbers of 12- to 24-bp repeats separated by repeating 6-bp sequences.Field studies aimed at defining the antigenic diversity of MSP2 have approached the problem by determining MSP2 gene structure by various forms of PCR. The rationale for this is that P. falciparum is haploid and MSP2 has been shown to be present in all laboratory and field isolates examined (8–10, 15). Most studies examining the distribution and frequency of different allelic forms of MSP2 have enumerated the presence of the allelic families (11, 12, 14). Whereas a skewed distribution of predominantly 3D7 family alleles exists among laboratory-adapted strains, in the field a more even distribution of FC27 and 3D7 alleles occurs. Often FC27 family alleles are more prevalent than 3D7 alleles, and novel FC27 and 3D7 family alleles have been found in field malaria strains (14, 16). Some field studies examining recurrent MSP2 infections have been performed, but these have classified MSP2 alleles on the basis of family and length of the central repeat region (7, 11, 14). This makes it difficult to form conclusions about the repertoire of repeat sequences in the circulating pool of parasites and to infer the possible action of immune responses to MSP2 repeats. We were interested to examine the sequences of MSP2 alleles circulating in an area of endemicity over time and to determine the persistence of various MSP2 alleles within a localized area. This study describes MSP2 genotypes from malaria-infected inhabitants of the Oksibil region of Irian Jaya and allows comparison of the variation in MSP2 sequences seen over a 2.5-year period within the region as a whole and in particular individuals.     

Progression of self-reported symptoms in laboratory animal allergy

BACKGROUND: Laboratory animal allergy is a common illness among workers exposed to laboratory animals and can progress to symptoms of asthma. OBJECTIVES: This study evaluates the continuum of disease from allergy symptoms to asthma symptoms in a dynamic cohort of workers exposed to animals in a pharmaceutical company. METHODS: Data arose from annual questionnaires administered to workers in a surveillance program established to monitor exposure to animals and the development of allergy. The life-table method was used to compare asthma-free survival between workers with and without symptoms of allergy. A Cox proportional hazards model was used to examine the effects of covariates on the development of asthma. RESULTS: A total of 603 workers contributed 2527.4 person-years to the study over the 12.3-year period. The probabilities of experiencing asthma symptoms by the 11th year of follow-up were 0.367 for workers with allergy symptoms and 0.052 for those without allergy symptoms. The hazard ratio for asthma symptoms when comparing workers with and without allergy symptoms was 7.39 (95% CI, 3.29-16.60) after adjustment for sex and family history of allergy. Female subjects developed asthma at a rate 3.4 times that of male subjects. CONCLUSIONS: This study supports the hypothesis that laboratory animal allergy symptoms are a major risk factor for the development of asthma. It also suggests a heightened risk of asthma for women who work with laboratory animals, a finding that has not been previously reported.     

P67L: a cystic fibrosis allele with mild effects found at high frequency in the Scottish population.

Only three mutant cystic fibrosis (CF) alleles have to date been established as conferring a dominant mild effect on affected subjects who are compound heterozygotes. We now add a fourth, P67L, which occurs on about 1.4% of Scottish CF chromosomes. Among 13 patients (12 unrelated) with this allele, the average age at diagnosis was 22.5 +/- 11.3 years. None of the cases had consistently raised sweat chloride concentrations, the average value being 57 +/- 9 mmol/l; 77% of the patients were pancreatic sufficient. When compared to three other established mild CF alleles, R117H, A455E, and 3849 + 10kb C-T, a compound heterozygote for P67L has minimal disease and clinical suspicions are unlikely to be confirmed other than by DNA typing.     

Identification of cathepsin C mutations in ethnically diverse papillon-Lefèvre syndrome patients

INTRODUCTION—Papillon-Lefèvre syndrome (PLS) is an autosomal recessive disorder characterised by palmoplantar keratoderma and severe, early onset periodontitis, which results from deficiency of cathepsin C activity secondary to mutations in the cathepsin C gene. To date, 13 different cathepsin C mutations have been reported in PLS patients, all of which are homozygous for a given mutation, reflecting consanguinity.
AIM—To evaluate the generality of cathepsin C mutations in PLS, we studied an ethnically diverse group of 20 unrelated families.
METHODS—Mutations were identified by direct automated sequencing of genomic DNA amplified for exonic regions and associated splice site junctions of the cathepsin C gene. Long range PCR was performed to determine the genomic structure of the cathepsin C gene.
RESULTS—The cathepsin C gene spans over 46 kb, with six introns ranging in size from 1.6 to 22.4 kb. Eleven novel mutations and four previously reported mutations were identified in affected subjects from 14 families. Missense mutations were most common (9/15), followed by nonsense mutations (3/15), insertions (2/15), and deletions (1/15). Among these 14 probands, two were compound heterozygotes. Affected subjects with transgressions of the dermal lesions onto the knees or elbows or both had mutations in both the pro- and mature regions of the enzyme, although most were in the mature region.
CONCLUSION—Mutations in the mature region of cathepsin C were more likely to be associated with the transgressions of the dermatological lesions, although the results were not statistically significant. A comprehensive list of all cathepsin C mutations described to date, representing 25 mutations from 32 families with PLS and related conditions, is also presented.


Keywords: cathepsin C; genetics; severe early onset periodontitis; hyperkeratosis     

Multilocular renal cysts in adults. Possible relationship to renal adenocarcinoma

Three grossly typical multilocular renal cysts are described. In one case, results from cytologic examination of a cyst aspirate were suggestive of malignancy. In this and the second case, histologic examination revealed cysts lined by attenuated to pump epithelium, with mild cytologic atypia and clear cytoplasm. The third case, arising in the clinical setting of chronic renal insufficiency, had the above histologic features as well as papillary proliferations and septal invasion by clear cells, interpreted as a renal adenocarcinoma. Although the preoperative evaluations in each case were suggestive of a multilocular cyst, a cystic or partially necrotic adenocarcinoma could not be ruled out. The concept of renal adenocarcinoma arising in a multilocular cyst is controversial. Because the natural evolution of multilocular cysts is indolent, these papillary and clear cell changes may represent a malignant neoplasm or a peculiar atypical hyperplasia.     

Improved quality-control detection of false-negative Pap smears using the Autopap 300 QC system

Federally-mandated quality control (QC) in Papanicolaou (Pap) smear testing requires rescreening of 10% of negative smears, to include cases selected randomly as well as smears from patients that may have a higher risk for developing cervical cancer based on clinical information. FDA approval of NeoPath's AutoPap 300 QC system (NeoPath, Inc., Redmond, WA) allows practical QC rescreening of all negatives. We tested the ability of AutoPap to help increase identification of detection errors compared to random 10%/high-risk selection. From March 1-August 30, 1997, we utilized AutoPap/high-risk status to select cases for manual rescreen, and compared the rate of identification of primary screening errors to that for the preceding year using 10% random selection/high-risk status. Of 35,027 smears accessioned, 31,240 (89.1%) were screened as negative and 7,965 were selected for manual rescreen. Of these, 353 were determined to be abnormal. Most abnormals identified by this protocol were classified as atypical squamous or glandular cells of undetermined significance (ASCUS or AGUS). However, 59 low-grade squamous intraepithelial lesions (LSIL) and 13 high-grade squamous intraepithelial lesions (HSIL), many with few abnormal cells, were also identified. These results represented an increase in pickup rate of false negative due to detection errors of 2.3-, 2.8- and 5.6-fold for atypical squamous or glandular cells of undetermined significance, LSIL, and HSIL, respectively, when accounting for the volume differences over the time period measured. Our findings strongly support the conclusions drawn from clinical trials of the AutoPap that false negatives due to detection error can be significantly reduced when using AutoPap as part of a routine quality control program.     

Accelerated elimination of N. brasiliensis from the small intestine after auto-anti-IgE induction.

Immunization of rats with a purified IgE myeloma (IR2) induced an auto-anti-IgE response. Such treatment inhibited total IgE levels in the serum of conventional IgE-producing rats (Marshall & Bell, 1985) and increased the number of mucosal mast cells (MMC) in the intestine. The present study has investigated the ability of auto-anti-IgE induction to influence the course of a Nippostrongylus brasiliensis infection, to modify IgE synthesis, or to affect the number of MMC in the intestine following infection. Auto-anti-IgE induction was found to have a surprising effect on worm elimination. IR2-immunized rats were able to rid themselves of this nematode with an accelerated tempo--a small but significant effect after primary infection, but a substantial enhancement of worm loss after reinfection. Auto-anti-IgE induction was not able to prevent the typical increase in IgE that accompanies an N. brasiliensis infection, nor did it alter the helminth-induced intestinal mastocytosis. When MMC degranulation was measured by assaying the serum levels of a specific rat mast protease (RMCP II) following secondary infection, the amount of RMCP II released was less in auto-anti-IgE-producing rats. These findings have implications for the importance of IgE, MMC and other cells of inflammation in an anti-parasitic response.     

SDF-1 induces IL-8 production and transendothelial migration of human cord blood-derived mast cells

BACKGROUND: Mast cell numbers and expression of chemokines are known to increase in the context of angiogenesis and inflammation, but the mechanisms by which this occurs are not understood. Stromal-derived factor-1 (SDF-1) is an important chemokine in angiogenesis and cell migration. The effects of SDF-1 on human mast cells were examined. METHODS: Expression of the SDF-1 receptor CXC chemokine receptor 4 (CXCR4) on mast cells was examined by RT-PCR and flow cytometry. The ability of labeled cord blood-derived mast cells to migrate across HUVEC monolayers in response to SDF-1 was determined. The cytokine and chemokine responses of cord blood-derived mast cells to SDF-1 treatment over 24 h were examined by ELISA. RESULTS: Cord blood-derived human mast cells expressed the CXCR4 receptor for SDF-1 and migrated across HUVEC monolayers in response to this chemokine. Treatment of cord blood-derived mast cells with SDF-1 did not induce degranulation or the production of several cytokines but did induce a highly selective IL-8 response. CONCLUSION: Human mast cells can both migrate across vascular endothelium and produce the pro-angiogenic chemokine IL-8 in response to SDF-1. These responses may be important in angiogenic processes.