Molecular Pathology of Severe Combined Immunodeficiency in Mice, Horses, and Dogs

Severe combined immunodeficiency (SCID) is an inherited disorder of humans, mice, horses, and dogs, in which affected individuals are incapable of generating antigen-specific immune responses. It occurs when lymphocyte precursors fail to differentiate into mature lymphocytes because of mutations within recombinase-activating genes 1 and 2 or within the genes encoding deoxyribonucleic acid (DNA)-dependent protein kinase (DNA-PK). It also occurs when differentiated lymphocytes are incapable of completing signal transduction pathways because of defects in cell surface receptors for interleukins (IL). A spontaneous mutation in DNA-PKcs of BALB/c mice results in SCID, as do experimentally induced mutations in RAG1 and RAG2. SCID in horses results from a spontaneous mutation in DNA-PKcs. Two molecular mechanisms account for SCID in dogs. Jack Russell Terriers have a mutation within the DNA-PKcs gene, whereas Cardigan Welsh Corgi and Basset Hound have different defects in the gene encoding the γ chain that is common to the receptors for IL-2, −4, −7, −9, −15, and −21. The location of the mutation within target genes influences the spectrum of diseases observed in affected animals.

T lymphocyte development and maturation in horses

Monoclonal antibodies specific for equine T lymphocyte subpopulations were produced and procedures for the continuous culture of equine lymphocytes were developed. These reagents and procedures were used to analyse the appearance, maturation and functions of T lymphocytes in normal horses and in T lymphocyte deficient horses with severe combined immunodeficiency (SCID). T lymphocytes appeared as early as the 75th day of fetal development and were normally distributed prior to birth of normal foals. Analysis of thymic T lymphocyte differentiation in SCID foals revealed the presence of both prothymocytes and mature thymocytes, but a virtual absence of cortical thymocytes. The data obtained support the hypothesis that two distinct pathways of T lymphocyte differentiation exist within the thymus. Although the gene defect in foals with SCID blocks the production of mature B and T lymphocytes, such foals do possess large granular lymphocytes which are cytotoxic following induction with interleukin 2. This suggests that lymphoid cells with natural killer cell activity are spared by the gene defect resulting in SCID in horses.

Detection of mucosally delivered antibody to Cryptosporidium parvum p23 in infected calves

We have developed an assay to detect mucosally delivered antibody to Cryptosporidium parvum sporozoite antigens. We absorbed a recombinant 23-kD sporozoite protein to polystyrene microspheres, and used flow cytometry to detect, titer, and determine the isotype of antibody to p23 that was shed in the feces of experimentally infected calves. Noninoculated calves have low levels of mucosal antibody to p23, with IgG1 as the predominant isotype. Antibody titers rise in inoculated calves as the animals recover from cryptosporidiosis. A calf that was naturally protected from cryptosporidiosis had mucosal IgM and IgG1 isotype anti-p23 antibodies prior to challenge with C. parvum oocysts. Ten days after challenge, the calf had high titers of IgM, IgA, IgG1, and IgG2 anti-p23 antibodies. Together, the data show that this method can be used to assess mucosally delivered antibody to C. parvum.

Excretion patterns of mucosally delivered antibodies to p23 in Cryptosporidium parvum infected calves

Fecal samples obtained at intervals from six calves with acute cryptosporidiosis contained antibodies of multiple isotypes to p23. IgM-, IgA-, and IgG(1)-isotype anti-p23 appeared before IgG(2)-isotype antibodies. All anti-p23 antibodies had declined by 2 months after infection. One calf that failed to shed oocysts following initial exposure developed IgG(1)-isotype anti-p23 antibodies. One calf that died following exposure to Cryptosporidium parvum oocysts lacked detectable anti-p23 antibodies. Re-inoculation with C. parvum resulted in a brief, marked recall response to p23.

Primary immunodeficiencies of horses

Primary immunodeficiency disorders are genetically determined failures of immune defense that increase susceptibility to infectious agents. This article reviews the salient features of equine primary immunodeficiency disorders, summarizes the molecular mechanisms of each disorder, and updates information that facilitates diagnosis and management of affected horses. The central theme is to encourage clinicians to ask, "I wonder if this horse has an underlying primary immunodeficiency disorder?" when caring for horses suffering from chronic and recurring infections and responding poorly to standard therapy.

A unique Babesia bovis spherical body protein is conserved among geographic isolates and localizes to the infected erythrocyte membrane

Using monoclonal antibody (mAb) 70/52.9, generated from a Babesia bovis fraction enriched for spherical body organelles, we have identified a 135-kDa protein containing an epitope conserved in B. bovis strains from Texas, Mexico, and Australia. The protein was localized to the spherical bodies of the babesial apical complex and was designated spherical body protein 3 (SBP3), according to the established nomenclature. Immunofluorescence studies showed binding of the 70/52.9 mAb to the infected-erythrocyte membrane region but not to their uninfected counterparts, demonstrating a host-cell association shared with the previously isolated B. bovis spherical body proteins, SBP1 and SBP2. Using mAb 70/52.9, the full-length cDNA encoding SBP3 was isolated from an expression library, sequenced, and oligonucleotide primers synthesized to amplify the genomic copy by polymerase chain reaction. The genomic copy contained no introns and was identical to the cDNA sequence with each containing a single, large open reading frame encoding a protein of 1089 residues. Analysis of the SBP3 amino acid sequence revealed no significant amino acid identity to SBP1 and SBP2 and a lack of repeated epitopes, a notable feature of the other two spherical body proteins. Labeled probes derived from the coding region of SBP3 hybridized to single fragments on Southern blots containing B. bovis genomic DNA indicating a single copy gene. With the identification of this third spherical body protein, which associates with the cytoplasmic face of the infected-erythrocyte membrane, a complement of distinct B. bovis proteins have been identified that are likely to contribute to intracellular survival, growth, and development for this parasite. The encoded protein should be valuable for functional investigations and evaluation of potential targets for host immunity.

Detection of equine antibodies to babesia caballi by recombinant B. caballi rhoptry-associated protein 1 in a competitive-inhibition enzyme-linked immunosorbent assay

A competitive-inhibition enzyme-linked immunosorbent assay (cELISA) was developed for detection of equine antibodies specific for Babesia caballi. The assay used recombinant B. caballi rhoptry-associated protein 1 (RAP-1) and monoclonal antibody (MAb) 79/17.18.5, which is reactive with a peptide epitope of a native 60-kDa B. caballi antigen. The gene encoding the recombinant antigen was sequenced, and database analysis revealed that the gene product is a rhoptry-associated protein. Cloning and expression of a truncated copy of the gene demonstrated that MAb 79/17.18.5 reacts with the C-terminal repeat region of the protein. The cELISA was used to evaluate 302 equine serum samples previously tested for antibodies to B. caballi by a standardized complement fixation test (CFT). The results of cELISA and CFT were 73% concordant. Seventy-two of the 77 serum samples with discordant results were CFT negative and cELISA positive. Further evaluation of the serum samples with discordant results by indirect immunofluorescence assay (IFA) demonstrated that at a serum dilution of 1:200, 48 of the CFT-negative and cELISA-positive serum samples contained antibodies reactive with B. caballi RAP-1. Four of five CFT-positive and cELISA-negative serum samples contained antibodies reactive with B. caballi when they were tested by IFA. These data indicate that following infection with B. caballi, horses consistently produce antibody to the RAP-1 epitope defined by MAb 79/17.18.5, and when used in the cELISA format, recombinant RAP-1 is a useful antigen for the serologic detection of anti-B. caballi antibodies.

Protection of calves against cryptosporidiosis with immune bovine colostrum induced by a Cryptosporidium parvum recombinant protein

The purpose of the study was to determine if immunization with a recombinant protein (rC7) of Cryptosporidium parvum would induce immune bovine colostrum that protected calves against cryptosporidiosis following oral challenge with C. parvum oocysts. Late gestation Holstein cows with low titers of antibody to the p23 antigen of C. parvum were immunized three times with 300 microg affinity purified rC7 C. parvum recombinant protein (immune cows), or left nonimmunized (control cows). Colostrum was obtained from each cow in both groups and partitioned into identical aliquots of pooled immune colostrum or pooled control colostrum. Twelve calves obtained at birth received either immune or control colostrum within the first 2 h, and again at 12 and 24 h of age. Each calf was challenged orally with 10(7) C. parvum oocysts at 12 h of age and monitored for signs of cryptosporidiosis. All six calves administered pooled control colostrum developed severe diarrhea (mean total fecal volume = 8447+/-5600 ml) and shed an average of 1.87+/-1.66 x 10(12) C. parvum oocysts. None of the six calves administered pooled immune colostrum developed diarrhea (mean total fecal volume = 740+/-750 ml, p < 0.05), and shed significantly fewer oocysts (3.05+/-2.26 x 10(9), p < 0.05). The absence of diarrhea and 2.79 log10 (99.8%) reduction in oocyst excretion indicates that immune bovine colostrum induced by immunization with C. parvum recombinant protein rC7 provided substantial protection against cryptosporidiosis in neonatal calves.

Cryptosporidium parvum sporozoite pellicle antigen recognized by a neutralizing monoclonal antibody is a beta-mannosylated glycolipid

The protozoan parasite Cryptosporidium parvum is an important cause of diarrhea in humans, calves, and other mammals worldwide. No approved vaccines or parasite-specific drugs are currently available for the control of cryptosporidiosis. To effectively immunize against C. parvum, identification and characterization of protective antigens are required. We previously identified CPS-500, a conserved, neutralization-sensitive antigen of C. parvum sporozoites and merozoites defined by monoclonal antibody 18.44. In the present study, the biochemical characteristics and subcellular location of CPS-500 were determined. CPS-500 was chloroform extractable and eluted with acetone and methanol in silicic acid chromatography, consistent with being a polar glycolipid. Following chloroform extraction and silicic acid chromatography, CPS-500 was isolated by high-pressure liquid chromatography for glycosyl analysis, which indicated the presence of mannose and inositol. To identify which component of CPS-500 comprised the neutralization-sensitive epitope recognized by 18.44, the ability of the monoclonal antibody to bind CPS-500 treated with proteases, or with alpha- or beta-glycosidases, was determined. Monoclonal antibody 18.44 did not bind antigen treated with beta-D-mannosidase but did bind antigen treated with alpha-D-mannosidase, other alpha- or beta-glycosidases, or a panel of proteases. These data indicated that the target epitope was dependent on terminal beta-D-mannopyranosyl residues. By immunoelectron microscopy, 18.44 binding was localized to the pellicle and an intracytoplasmic tubulovesicular network in sporozoites. Monoclonal antibody 18.44 also bound to antigen deposited and released onto substrate over the course travelled by gliding sporozoites and merozoites. Surface localization, adhesion and release during locomotion, and neutralization sensitivity suggest that CPS-500 may be involved in motility and invasion processes of the infective zoite stages.

Equine SCID: mechanistic analysis and comparison with murine SCID

V(D)J rearrangement is the molecular mechanism by which an almost limitless number of unique immune receptors is generated. V(D)J rearrangement involves two DNA breaks and religations resulting in two DNA joints; coding and signal joints. If V(D)J recombination is impaired (as in murine SCID (C.B-17 mouse] or RAG [Recombinase Activating Genes) deficient mice), B lymphocyte and T lymphocyte development is blocked and severe immunodeficiency results. The first animal model of SCID was reported in Arabian foals in 1973. Recently we demonstrated that the mechanistic defect in SCID foals is V(D)J recombination. However, the impairment of V(D)J recombination in SCID foals is phenotypically distinct from SCID mice in that both signal and coding joint ligation are impaired. Furthermore, though equine SCID and murine SCID have definite phenotypic differences, both defects are likely to be the result of defective expression of the catalytic subunit of the DNA-dependent protein kinase.

IL-4 protects adult C57BL/6 mice from prolonged Cryptosporidium parvum infection: analysis of CD4+alpha beta+IFN-gamma+ and CD4+alpha beta+IL-4+ lymphocytes in gut-associated lymphoid tissue during resolution of infection

Resistance of adult C57BL/6 mice to severe Cryptosporidium parvum infection is dependent on CD4+alpha beta+ TCR lymphocytes. In this study, we demonstrated that treatment with anti-IFN-gamma mAb extended oocyst excretion 18 days longer, and anti-IL-4 mAb extended oocyst excretion at least 11 days longer than isotype control mAb treatment. Analysis of the specific activity of anti-IFN-gamma mAb present in treated mouse sera suggested that IFN-gamma may have a limited role in the resolution phase of infection. Changes were also documented in numbers of CD4+alpha beta+IFN-gamma+ and CD4+alpha beta+IL-4+ lymphocytes in Peyer's patches and intraepithelium of adult C57BL/6 mice during resolution of C. parvum infection. Resistance to initial severe infection was associated with CD4+alpha beta+IFN-gamma+ lymphocytes, and eventual resolution of infection was associated with CD4+alpha beta+IL-4+ lymphocytes. Analysis of cytokine expression following in vitro stimulation with C. parvum Ags during resolution of infection demonstrated consistent increases in CD4+alpha beta+IL-4+ lymphocytes, but not CD4+alpha beta+IFN-gamma+ lymphocytes. The relevance of CD4+alpha beta+IL-4+ lymphocytes in protection against C. parvum was then evaluated in C57BL/6 IL-4 gene knockout mice (IL-4(-/-)). Adult IL-4(-/-) mice excreted oocysts in feces approximately 23 days longer than IL-4(+/+) mice. Further, anti-IFN-gamma mAb treatment increased the severity and the duration of infection in IL-4(-/-) mice compared with those in IL-4(+/+) mice. Together, the data demonstrated that IFN-gamma was important in the control of severity of infection, and either IFN-gamma or IL-4 accelerated termination of infection. However, neither IL-4 nor IFN-gamma was required for the final clearance of infection from the intestinal tract of adult mice.

CD8 dimer usage on alpha beta and gama delta T lymphocytes from equine lymphoid tissues

Eight murine monoclonal antibodies (mAb) were used to identify the equine CD8 alpha or CD8 beta chains and to define the expression of these chains on lymphocytes from various lymphoid tissues. CD8 alpha was a 39 kDa protein and CD8 beta was a 32 kDa protein. Both chains were expressed on most of the CD8+ T lymphocytes in the peripheral blood, spleen, thymus, mesenteric lymph nodes and ileal intraepithelial lymphocytes (IEL), however, in each lymphoid compartment a percentage of lymphocytes expressed only the CD8 alpha chain. The largest percentage of CD8 alpha alpha expressing T lymphocytes was 37.7% of the IELs. Purified T lymphocytes from the ileum expressing CD8 alpha beta co-expressed the alpha beta T cell receptor (TCR). In contrast, purified CD8+ T lymphocytes from the PBMC co-expressed either the alpha beta or gamma delta TCR by RT-PCR. Use of pooled anti-CD8 alpha mAb of the murine IgG2a isotype and rabbit complement resulted in lysis of the entire CD8 expressing population in peripheral blood mononuclear cells (PBMC). These results indicated that CD8 dimer usage by equine T lymphocytes is similar to other species and that the mAb described can be further used to separate equine CD8+ T lymphocyte subsets from the lymphoid tissues to define their function in protection against viral and other infections.

Genetic and biochemical analysis of erythrocyte-stage surface antigens belonging to a family of highly conserved proteins of Babesia equi and Theileria species

Erythrocyte-stage Babesia equi expresses a 34-kDa immunodominant antigen recognized by antibody from persistently infected horses worldwide. This erythrocyte-stage surface protein, equi merozoite antigen-1 (EMA-1) is encoded by a single copy gene, and was previously shown to share 33% amino acid identity with similar sized proteins of Theileria sergenti and T. buffeli. A mean homology of 31% amino acid identity extends to similar sized proteins of T. parva, T. annulata and T. mutans. Genomic and cDNA copies of a second B. equi gene, ema2 were cloned. The single copy ema2 gene encodes a 30-kDa protein (EMA-2) that shares 52% amino acid identity with EMA-1. EMA-2 also shares a mean amino acid identity of 31% with proteins of similar molecular mass from Theileria species. EMA-1 and EMA-2 each contain a glycosylphosphatidylinositol anchor. These unique erythrocyte-stage surface proteins of B. equi and Theileria species lack antigenic repeats, and excluding the signal peptide, contain one or no cysteines. Consistent with the hypothesis that this family of proteins interacts with the erythrocyte surface, the T. species proteins possess a basic isoelectric point. The B. equi proteins have acidic isoelectric points, but 24-mer peptides within them have strongly basic net charges.

Evaluation of a test for identification of Arabian horses heterozygous for the severe combined immunodeficiency trait

OBJECTIVE

To determine whether a recently developed test would correctly identify horses heterozygous for the severe combined immunodeficiency (SCID) trait.

DESIGN

Case series.

ANIMALS

17 healthy Arabian horses that had previously produced foals with SCID, 1 healthy Arabian foal whose dam and sire had produced foals with SCID, 4 foals with SCID, and 1 healthy non-Arabian foal.

PROCEDURE

DNA was extracted from leukocytes or fibroblasts, amplified by means of polymerase chain reaction, and hybridized with probes specific for the normal and mutant alleles of the catalytic subunit of DNA-dependent protein kinase, the factor whose absence is responsible for SCID in Arabian foals.

RESULTS

Amplified DNA from the healthy non-Arabian foal hybridized only to the probe specific for the normal allele, whereas amplified DNA from the 4 foals with SCID hybridized only to the probe specific for the mutant allele. Amplified DNA from the 2 stallions and 15 mares hybridized with both probes, as did amplified DNA from the healthy foal whose dam and sire had previously produced foals with SCID, indicating that these horses were all heterozygous for the SCID trait.

CLINICAL IMPLICATIONS

Results suggest that the genetic test will be useful in identifying Arabian horses heterozygous for the SCID trait and foals with SCID, provided that all Arabian horses with SCID have the same genetic mutation.

Babesia bovis: identification of immunodominant merozoite surface proteins in soluble culture-derived exoantigen

Babesia bovis merozoite proteins presenting as exoantigens in in vitro culture supernatants have been characterized. Bovine antisera to B. bovis exoantigens were used to immunoprecipitate [35S]-methionine metabolically labeled or lactoperoxidase-catalyzed radioiodinated B. bovis merozoite proteins. A total of 24 metabolically labeled proteins ranging in molecular weight from 24,000 to 225,000 Da and 9 radioiodinated proteins with molecular weights varying between 24,000 and 225,000 Da were identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Monoclonal antibodies to B. bovis merozoite surface proteins were also used to immunoprecipitate metabolically labeled exoantigens directly from in vitro culture supernatants. These results demonstrate epitopes from at least nine merozoite surface proteins present in the exoantigen fraction, among which are the recently characterized major surface antigens 1 and 2, rhoptry-associated protein 1, and spherical body protein 2.

A kinase-negative mutation of DNA-PK(CS) in equine SCID results in defective coding and signal joint formation

The equine SCID defect is more severe than its murine counterpart in that SCID foals are incapable of forming either coding or signal joints, whereas SCID mice manifest normal signal joint formation. To determine the basis of this difference and whether DNA-dependent kinase, catalytic subunit (DNA-PK(CS)), is involved in signal joint formation, equine DNA-PK(CS) transcripts were cloned and sequenced from normal and SCID cell lines. In the mutant allele, a frame-shift mutation truncates the protein N terminal of the domain with homology to the phosphatidylinositol 3-kinase family resulting in complete absence of full length DNA-PK(CS) and accounting for the kinase-negative phenotype of these cells; the mutation in SCID mice allows for some DNA-PK(CS) expression. The difference in DNA-PK(CS) expression in SCID mice and foals explains the more severe phenotype of equine SCID, and definition of DNA-PK(CS) as the defect in equine SCID demonstrates that DNA-PK(CS) is required for both coding and signal joint formation.

A kinase-negative mutation of DNA-PK(CS) in equine SCID results in defective coding and signal joint formation

The equine SCID defect is more severe than its murine counterpart in that SCID foals are incapable of forming either coding or signal joints, whereas SCID mice manifest normal signal joint formation. To determine the basis of this difference and whether DNA-dependent kinase, catalytic subunit (DNA-PK(CS)), is involved in signal joint formation, equine DNA-PK(CS) transcripts were cloned and sequenced from normal and SCID cell lines. In the mutant allele, a frame-shift mutation truncates the protein N terminal of the domain with homology to the phosphatidylinositol 3-kinase family resulting in complete absence of full length DNA-PK(CS) and accounting for the kinase-negative phenotype of these cells; the mutation in SCID mice allows for some DNA-PK(CS) expression. The difference in DNA-PK(CS) expression in SCID mice and foals explains the more severe phenotype of equine SCID, and definition of DNA-PK(CS) as the defect in equine SCID demonstrates that DNA-PK(CS) is required for both coding and signal joint formation.

Control of equine infectious anemia virus is not dependent on ADCC mediating antibodies

Horses infected with equine infectious anemia virus (EIAV) have recurrent episodes of viremia which are eventually controlled, but the immune mechanisms have not been identified. Antibodies were detected to the surface of EIAV-infected cells within 1 month postinfection and remained for at least 3.5 years postinfection. These antibodies recognized cell surface-exposed envelope (Env) glycoproteins, but could not mediate antibody dependent cellular cytotoxicity (ADCC) using EIAV-WSU5-infected equine kidney (EK) cells as targets and peripheral blood mononuclear cells (PBMC) or polymorphonuclear cells (PMN) as effector cells. Furthermore, purified IgG antibodies from horses infected with either EIAV-WSU5 or EIAV-Wyo did not mediate ADCC of infected target cells. Armed effector cells could not be detected in infected horse blood nor could effector cells be prearmed by incubation with serum antibodies to cell surface antigens. The use of EIAV-WSU5-infected equine macrophages as target cells did not result in ADCC. In contrast, serum antibody from EHV-1 vaccinated horses and PBMC or PMN as effector cells caused ADCC of EHV-1-infected EK cells. These results indicate that ADCC is not involved in the control of EIAV in carrier horses.

Anaplasma marginale major surface protein 3 is encoded by a polymorphic, multigene family

The immunodominant surface protein, MSP3, is structurally and antigenically polymorphic among strains of Anaplasma marginale. In this study we show that a polymorphic multigene family is at least partially responsible for the variation seen in MSP3. The A. marginale msp3 gene msp3-12 was cloned and expressed in Escherichia coli. With msp3-12 as a probe, multiple, partially homologous gene copies were identified in the genomes of three A. marginale strains. These copies were widely distributed throughout the chromosome. Sequence analysis of three unique msp3 genes, msp3-12, msp3-11, and msp3-19, revealed both conserved and variant regions within the open reading frames. Importantly, msp3 contains amino acid blocks related to another polymorphic multigene family product, MSP2. These data, in conjunction with data presented in previous studies, suggest that multigene families are used to vary important antigenic surface proteins of A. marginale. These findings may provide a basis for studying antigenic variation of the organism in persistently infected carrier cattle.

Activation of intestinal intraepithelial T lymphocytes in calves infected with Cryptosporidium parvum

The objective of this study was to identify disease-related changes in lymphocyte populations within ileal mucosae of calves with cryptosporidiosis. Groups of five neonatal calves were orally infected at 3 days of age with 10(8) oocysts and maintained in enteric-pathogen-free conditions until clinical disease was established or until the animals had recovered from disease. Age-matched uninfected calves were used for comparison. Ileal mucosal lymphocytes were collected, quantitated, and phenotyped to determine whether changes in lymphocyte composition occurred in infected animals. We observed significantly larger numbers of intraepithelial CD8+ T lymphocytes in ileal mucosae from acutely infected calves compared with those from control animals. In addition, a proportion of intraepithelial CD4+ T cells from acutely infected calves coexpressed CD25, whereas there was an absence of coexpressed CD25 on CD4+ T cells from control calves. Ex vivo reverse transcriptase PCR of RNA from intraepithelial lymphocytes from control calves showed a cytokine expression pattern consisting of tumor necrosis factor alpha (TNF-alpha) and gamma interferon (IFN-gamma), while intraepithelial lymphocytes from calves with cryptosporidiosis expressed IFN-gamma but not TNF-alpha. Together, the results indicate that changes occur in the ileal intraepithelial lymphocyte population coincidently with Cryptosporidium parvum-induced enteric disease.

Monoclonal antibodies to surface-exposes proteins of Mycoplasma mycoides subsp. mycoides (small-colony strain), which causes contagious bovine pleuropneumonia

Outbreaks of bovine pleuropneumonia caused by small-colony strains of Mycoplasma mycoides subsp. mycoides occur in Africa, and vaccination is used for control. Since protein subunits are needed to improve multivalent vaccines, monoclonal antibodies (MAbs) were made to facilitate protein identification and isolation. Eleven immunoglobulin M MAbs derived from mouse spleen donors immunized with disrupted whole organisms bound periodate-sensitive epitopes on externally exposed polysaccharide. Seven of these MAbs caused in vitro growth inhibition of M. mycoides subsp. mycoides; however, reaction with carbohydrate epitopes prevented their use in identifying proteins. Ten additional MAbs from mouse spleen donors immunized with Triton X-114-phase integral membrane proteins reacted with periodate-insensitive, proteinase K-sensitive epitopes. These MAbs were classified into three groups based on immunoblots of Triton X-114-phase proteins. One group reacted with 96-, 16-, and 15-kDa proteins. Another group reacted with 26-, 21-, and 16-kDa proteins, while a third group reacted only with 26- and 21-kDa proteins. One MAb from each group reacted with trypsinsensitive epitopes on live organisms, yet none caused in vitro growth inhibition. Representative MAbs reacted with all small-colony strains in immunoblots and did not react with large colony strains. However, these MAbs were not specific for small-colony strains, as proteins from two other M. mycoides cluster organisms were identified. Nevertheless, MAbs to surface-exposed epitopes on integral membrane proteins will be useful for isolation of these proteins for immunization, since one or more might induce growth-inhibiting antibodies or other protective responses.

A cloned gene of Cryptosporidium parvum encodes neutralization-sensitive epitopes

Two mAb, C6B6 and 7D10, each significantly reduced infection of mice by Cryptosporidium parvum and reacted with a 23-kDa glycoprotein (p23) of geographically disperse C. parvum isolates. The antibodies were used to identify plaques in a cDNA library prepared from C. parvum sporozoite mRNA. cDNA insert sequences from positive plaques were determined and used to isolate additional clones encoding p23 coding sequences. A consensus open reading frame of 333 base pairs, encoding 111 amino acids, was identified in this collection of cDNAs. The predicted amino acid sequence contained one N-glycosylation site, but lacked hydrophobic membrane spanning regions. Epitope mapping revealed that mAb 7D10 defines the linear epitope QDKPAD which occurs twice in the C terminal region of the peptide encoded by the ORF. This same C terminal peptide region contains a non-linear epitope bound by mAb C6B6. Serum from mice immunized with synthetic C terminal peptide reacted with sporozoite p23. The occurrence of neutralization-sensitive epitopes encoded by defined regions of the C. parvum genome suggests that recombinant proteins or synthetic peptides containing these epitopes may prove useful for inducing immune responses that diminish infection.

Haemonchus contortus GA1 antigens: related, phospholipase C-sensitive, apical gut membrane proteins encoded as a polyprotein and released from the nematode during infection

It was previously shown that the Haemonchus contortus apical gut surface proteins p46, p52, and p100 induced protective immunity to challenge infections in goats. Here, it is shown that the three proteins are all encoded by a single gene (GA1) and initially expressed in adult parasites as a polyprotein (p100GA1). p46GA1 and p52GA1 are related proteins with 47% sequence identity, including a cysteine-containing region, which appears to confer secondary structure to these proteins, and a region with sequence similarity to bacterial Tolb proteins. GA1 protein expression is regulated during the life cycle at the level of transcript abundance. Only p52GA1 has characteristics of a glycosylinositolphospholipid membrane-anchored protein. However, both p46GA1 and p52GA1 were released from the gut membrane by phosphatidylinositol specific-phospholipase C, suggesting that p46GA1 membrane association depends on interactions with a glycosylinositolphospholipid gut membrane protein. Finally, GA1 proteins occur in abomasal mucus of infected lambs, demonstrating possible presentation to the host immune system during H. contortus infection. The results identify multiple characteristics of the GA1 proteins that should be considered for design of recombinant antigens for vaccine trials and that implicate a series of cellular processes leading to modification and expression of GA1 proteins at the nematode apical gut surface.

A Babesia bovis 225-kilodalton spherical-body protein: localization to the cytoplasmic face of infected erythrocytes after merozoite invasion

A 225-kDa Babesia bovis protein occurs on the cytoplasmic side of infected-erythrocyte membranes. Here it is demonstrated that the 225-kDa protein localizes to spherical-body organelles of merozoites. Organelles consistent in size and shape with spherical bodies were isolated between 1.17 and 1.21 g/cm(3) in a sucrose density gradient. Organelles consistent with rhoptries and micronemes were also present in fractions from 1.17 to 1.19 g/cm(3). Antisera generated by immunizing mice with the fraction (1.20 to 1.21 g/cm(3)) most enriched for spherical bodies reacted predominantly with spherical bodies in B. bovis merozoites. A monoclonal antibody generated from this immunization (70/97.14) recognized an epitope that occurs in the repeat region of the 225-kDa protein (now referred to as SBP2). Monoclonal antibody 70/97.14 bound to merozoite spherical bodies, vesicles in infected-host cytoplasm, and the cytoplasmic face of the infected-erythrocyte membrane. These results indicate that spherical-body proteins become associated with the host membrane via transport through the erythrocyte cytoplasm after intracellular invasion.

Identification of gamma delta T lymphocyte subsets that populate calf ileal mucosa after birth

Ileal intraepithelial and lamina propria lymphocytes from newborn, 1.5-week-old, and 3-week-old calves were compared to determine to what extent the mucosa becomes populated after birth. Single and dual fluorescence flow cytometry were used with monoclonal antibodies to bovine (Bo) CD molecules to identify lymphocyte subpopulations. Few ileal mucosal lymphocytes were present in calves at birth. However, by 1.5 weeks of age, the villi were populated with large numbers of lymphocytes, and by 3 weeks of age, the numbers had increased further. These included a prominent subpopulation of gamma delta T cells. Several subsets of gamma delta T cells populated ileal mucosa after birth. The predominant subset coexpressed BoCD2, and a smaller subset coexpressed BoCD8. WC1+ gamma delta T cells comprised the smallest subset. All gamma delta T cell subsets coexpressed ACT2, a molecule expressed on activated WC1+ and WC1- gamma delta T cells from cattle.

Equine severe combined immunodeficiency: a defect in V(D)J recombination and DNA-dependent protein kinase activity

V(D)J rearrangement is the molecular mechanism by which an almost infinite array of specific immune receptors are generated. Defects in this process result in profound immunodeficiency as is the case in the C.B-17 SCID mouse or in RAG-1 (recombination-activating gene 1) or RAG-2 deficient mice. It has recently become clear that the V(D)J recombinase most likely consists of both lymphoid-specific factors and ubiquitously expressed components of the DNA double-strand break repair pathway. The deficit in SCID mice is in a factor that is required for both of these pathways. In this report, we show that the factor defective in the autosomal recessive severe combined immunodeficiency of Arabian foals is required for (i) V(D)J recombination, (ii) resistance to ionizing radiation, and (iii) DNA-dependent protein kinase activity.

Babesia bigemina: identification of B cell epitopes associated with parasitized erythrocytes

Rhoptries are involved in host cell invasion and rhoptry polypeptides, including the Babesia bigemina rhoptry-associated protein-1 (RAP-1), are targets for protective immune responses. Polyclonal antisera produced against isolated rhoptries is directed predominantly against RAP-1 and reacts with both the merozoite and the membrane of parasitized erythrocytes. To determine whether these B cell epitopes associated with the parasitized erythrocyte are derived from RAP-1 or, alternatively, from previously undetected merozoite polypeptides, monoclonal antibodies (mAbs) were generated from mice immunized with rhoptries isolated from the JG-29 clone of the Mexico strain. The anti-RAP-1 mAbs bound only merozoites in a punctate immunofluorescence pattern. A second group of four mAbs, none of which were reactive with RAP-1, bound the parasitized erythrocyte. Two of these latter mAbs, 64/44.17.3 and 64/05.7.2, reacted only with parasitized erythrocytes that had been permeabilized. MAb 64/44.17.3 bound a 54-kDa merozoite polypeptide while 64/05.7.2 bound a > or = 225-kDa merozoite polypeptide. MAbs 64/32.8.5 and 64/38.5.3 recognized epitopes on 17.5- and 76-kDa polypeptides exposed on the external surface of intact parasitized erythrocytes. The results indicate that the identified RAP-1 epitopes are not associated with the erythrocyte cytoskeleton or membrane and that anti-RAP-1 immunity is most likely generated against the free merozoite. All new mAbs reacted with every B. bigemina strain tested (Mexico, Puerto Rico, St. Croix, Texcoco, Jaboticabal). The conservation of RAP-1 epitopes among these strains supports the continued testing of RAP-1 as a vaccine component. In addition, the identification of epitopes expressed on the surface of erythrocytes infected with all five strains provides new candidate immunogens.

Monoclonal antibody to a conserved epitope on proteins encoded by Babesia bigemina and present on the surface of intact infected erythrocytes

To define Babesia bigemina-specific antigens on the surface of infected erythrocytes, monoclonal antibodies (MAbs) were identified by live-cell immunofluorescence. As determined by live-cell immunofluorescence, two MAbs made to the Mexico strain reacted with the Mexico strain and three Kenya strains, while three MAbs made to the Kenya-Ngong strain reacted with the Kenya strains but not the Mexico strain. Binding of MAb 44.18 (made to the Mexico strain) to a strain-common epitope was confirmed by immunoelectron microscopy and by surface-specific immunoprecipitation of [35S]methionine-labeled proteins (200, 28, and 16 kDa in size), which also demonstrated that the MAb recognized an epitope on proteins encoded by B. bigemina. In immunoblots, the MAb bound to predominant antigens with sizes of 200 and 220 kDa in erythrocyte lysates infected with strains from Puerto Rico, St. Croix, Texcoco (Mexico), Kenya, and Mexico. Major antigens with sizes of 200 and 220 kDa were isolated from a MAb 44.18 affinity matrix. Calf serum antibodies to these isolated antigens bound to erythrocytes infected with either the Mexico or Kenya strains as determined by live-cell immunofluorescence, allowing the conclusion that at least one conserved surface epitope was recognized. Calf serum antibodies identified major labeled proteins with sizes of 200 and 72 kDa by surface-specific immunoprecipitation, and infected erythrocytes sensitized with these antibodies were phagocytized by cultured bovine peripheral blood monocytes. These results provide a rationale for evaluating antigens identified by MAb 44.18 individually and as components of subunit vaccines.

Attempts to protect severe combined immunodeficient (scid) mice with antibody enriched for reactivity to Cryptosporidium parvum surface antigen-1

Cryptosporidium parvum is a protozoal pathogen which infects the gastrointestinal epithelium of mammals causing diarrhoea, the duration and severity of which is determined by the immunocompetency of the host. Currently, there is no effective treatment or prevention. We evaluated the ability of surface antigen-1 (SA-1), defined as those antigens recognized by neutralizing mAb 17.41, to elicit a protective antibody response when used as an immunogen. A SA-1 enriched fraction was obtained by immunoaffinity chromatography and was used to immunize a naive Holstein calf. SA-1 immune serum from this calf detected C. parvum epitopes to a 1:10,000 dilution in a dot blot assay, and sporozoite surface epitopes at a 1:10,000 dilution in a live immunofluorescence assay. Western blot analysis showed that SA-1 immune bovine serum recognized a similar pattern of C. parvum antigens as the defining mAb 17.41. Oral passive transfer of SA-1 immune bovine serum did not protect severe combined immunodeficient (scid) mice or suckling BALB/c mice from initial infection with C. parvum, or terminate a persistent infection in scid mice.

Effect of surface antigen-1 (SA-1) immune lymphocyte subsets and naive cell subsets in protecting scid mice from initial and persistent infection with Cryptosporidium parvum

We tested the hypothesis that adoptive transfer of immune spleen cell subsets from Cryptosporidium parvum antigen immunized, immunocompetent BALB/c mice would prevent initial infection or terminate persistent infection in severe combined immunodeficient (scid) mice. Cell donor mice were immunized with either solubilized C. parvum oocysts and sporozoites (positive control) or a surface antigen-1 (SA-1) enriched C. parvum antigen fraction. Both groups of BALB/c cell donor mice immunized with C. parvum antigens had increased antibody titers and lymphoproliferative responses when compared with negative control mice injected with phosphate buffered saline and adjuvant. Intravenous adoptive transfer of 5 x 10(6) cells of each cell subset (spleen cells, CD4 T and B lymphocytes, CD4 T lymphocytes or B lymphocytes) derived from immunized adult BALB/c donor mice did not protect scid mice against initial infection of the gastrointestinal epithelium with C. parvum, despite flow cytometric evidence of CD4 T lymphocyte engraftment in the spleen and detectable levels of C. parvum-specific serum antibody. In contrast, intravenous injection of either naive or immune CD4 T and B lymphocytes combined, or CD4 T lymphocytes alone, terminated persistent C. parvum infection in scid mice. Intestinal infectivity scores were significantly reduced by 9 days post-engraftment in all groups and continued to decline throughout the remainder of the experiment. Flow cytometric analysis demonstrated significantly increased CD4 T lymphocytes in the spleens of recipient scid mice when compared with infected scid mice receiving no cells. Cryptosporidium parvum-specific antibody was detected on day 12 post engraftment in mice receiving SA-1 immune CD4 T and B lymphocytes but was not detectable in mice receiving naive cell subsets.

Conserved recombinant antigens of Anaplasma marginale and Babesia equi for serologic diagnosis

The competitive inhibition ELISA (CI-ELISA) format overcomes problems associated with antigen purity since the specificity of the CI-ELISA depends solely on the monoclonal antibody (mAb) used. Therefore, the CI-ELISA format is well suited for use with recombinant antigens. Molecular clones expressing a conserved 19 kDa protein of Anaplasma marginale and a 34 kDa protein of Babesia equi were derived and characterized. The 19 kDa A. marginale protein, conserved in all recognized Anaplasma species, and present in the infected tick salivary gland, was reactive with all bovine immune sera tested. The 34 kDa B. equi protein contains a protein epitope bound by antibody in equine immune sera from 19 countries. Monoclonal antibodies reactive with these proteins were derived and applied with recombinant copies of the 19 kDa A. marginale and 34 kDa B. equi proteins in a CI-ELISA format.

Comparison of Cryptosporidium parvum and Cryptosporidium wrairi by reactivity with monoclonal antibodies and ability to infect severe combined immunodeficient mice

Twenty-three monoclonal antibodies raised to Cryptosporidium parvum and 12 raised to C. wrairi reacted with equal intensity with the heterologous species. Despite demonstration of a close immunologic relationship between these two species, C. wrairi did not induce persistent infection in severe combined immunodeficient mice as did C. parvum.

Antigenic, morphologic, and molecular characterization of new Ehrlichia risticii isolates

Ehrlichia risticii causes an acute infectious disease in horses called Potomac horse fever. To investigate the biological diversity of E. risticii organisms, nine E. risticii isolates derived from the peripheral blood monocytes of clinically sick horses in Ohio and Kentucky during the summers of 1991 and 1993 were compared with Illinois and Virginia isolates originally obtained from horses in Maryland in 1984. Seven of the nine isolates (081, 606, 380, 679, As, Co, and Ov) formed large morulae (tightly packed inclusions of ehrlichial organisms). The remaining isolates, including 1984 isolates, were individually dispersed or formed small morulae in the cytoplasm of P388D1 cells. In Western blot (immunoblot) analysis with four equine and one rabbit polyclonal anti-E. risticii sera, these recent E. risticii isolates showed patterns of antigenic proteins distinct from those of the 1984 isolates and could be divided into three groups: (i) 081; (ii) 606, 022, 067, 380, and 679; and (iii) As, Co, and Ov. By indirect fluorescent antibody labeling with two panels of murine anti-E. risticii (Illinois and Maryland isolates) monoclonal antibodies, isolate 081 was not labeled with any of 20 monoclonal antibodies tested. The remaining isolates were not labeled with several monoclonal antibodies. The digestion pattern with one of the restriction enzymes, AvaII, of the PCR-amplified partial 16S rRNA gene of E. risticii from all Kentucky isolates (As, Co, and Ov) was different from that of Illinois, Virginia, and six Ohio isolates. These results indicate the presence of distinct variants of E. risticii which vary significantly in morphology, antigenic composition, and the base sequence of the 16S rRNA gene.

Antibody response to a Babesia bigemina rhoptry-associated protein 1 surface-exposed and neutralization-sensitive epitope in immune cattle

Protective immunity against Babesia bigemina is hypothesized to involve antibodies directed against merozoite surface-exposed epitopes. Levels of antibody against a rhoptry-associated protein 1 (RAP-1) B-lymphocyte epitope, defined by surface-reactive and inhibitory monoclonal antibodies, in immune cattle sera were determined. All cattle produced antibodies to the epitope; however, there was limited correlation between immune protection induced by infection or RAP-1 immunization and the level of antibody to the neutralization-sensitive B-lymphocyte epitope examined.

Specific immune responses are required to control parasitemia in Babesia equi infection

Horses possessing a normal immune system and spleen often control infection caused by Babesia equi. However, splenectomized horses are unable to control B. equi infection and usually succumb to the infection. To investigate the role of the spleen in the control of B. equi infection in the absence of specific immune responses, two 1-month-old foals with severe combined immunodeficiency (SCID) and two age-matched normal foals were inoculated with B. equi. The SCID foals became febrile seven days postinoculation and developed terminal parasitemias of 41 and 29%. The SCID foals had greater than 50% decreases in indices of total erythrocytes, packed-cell volumes, and hemoglobin concentrations. Both SCID foals were euthanized in extremis at 10 days postinoculation. As expected, the serum of the SCID foals lacked detectable antibodies to B. equi antigens. In contrast, the normal foals inoculated with B. equi produced detectable anti-erythrocyte-stage parasite antibodies by 7 days and controlled clinical disease by 12 days postinoculation. Although SCID foals lack functional T and B lymphocytes, they do possess complement, macrophages, granulocytes, and natural killer cells, as well as a spleen. Therefore, the data indicate that specific immune responses are required to control B. equi parasitemia but are not required for erythrocyte lysis in infected horses. Furthermore, the spleen is not able to control B. equi parasitemia in the absence of specific immune responses to parasite antigens.

Corticosteroid immunosuppression and monoclonal antibody-mediated CD5+ T lymphocyte depletion in normal and equine infectious anaemia virus-carrier horses

The immune control of chronic equine infectious anaemia (EIA) lentiviral infection was investigated by specifically depleting CD5+ T lymphocytes in vivo with monoclonal antibody (MAb) or by immunosuppression with corticosteroids. MAb was given at 25 to 50 mg/day intravenously for 11 days. Murine IgG1 anti-equine CD2 MAb (n = 2 horses) or IgG1 (n = 2) and IgG2a control MAb (n = 2 normal; 2 EIA-infected) did not deplete CD2+ T lymphocytes in horses. Horses given murine IgG2a anti-CD5 MAb HB19A (n = 4 normal; 5 EIA-infected) had depletion of peripheral blood CD5+ T lymphocytes during treatment. These horses, however, maintained a residual population of CD2+ T lymphocytes [15 (+/- 3)% of pretreatment numbers] that did not express CD5 but expressed either CD4 or CD8. These antigenically modulated CD5- T lymphocytes responded normally in vivo to intradermal inoculation with phytohaemagglutinin and in vitro to allogeneic leukocyte stimulation in one-way mixed lymphocyte reactions. EIA virus-infected horses (n = 5) did not develop recrudescent viraemia or disease following in vivo CD5+ T lymphocyte depletion. Immunosuppression of EIA virus-infected horses with corticosteroids (1 mg/kg body weight/day, intravenously for 9 days) resulted in detectable recrudescent EIA viraemia in 6/11 horses (55%) and recrudescent disease in 9/11 horses (82%). Normal horses (n = 3) treated with corticosteroids developed no clinical disease. These results demonstrate that the use of murine IgG2a MAbs to appropriate equine lymphocyte antigens will facilitate in vivo investigation of the role of T lymphocyte subpopulations in the control of EIA or other important equine diseases.

Effect of spleen cell populations on resolution of Cryptosporidium parvum infection in SCID mice

Persistent infection was established in SCID mice given 10(7) Cryptosporidium parvum oocysts. Nine groups of infected SCID mice were inoculated with 10(6), 10(5), or 10(4) total spleen cells, CD8-depleted spleen cells, or CD4-depleted spleen cells from naive BALB/c donors. Infection was significantly reduced in all treatment groups. The most profound effect occurred with spleen cell preparations containing CD4 T lymphocytes but depleted of CD8 T lymphocytes.

Major histocompatibility complex-restricted CD8+ cytotoxic T lymphocytes from horses with equine infectious anemia virus recognize Env and Gag/PR proteins

Cytotoxic T lymphocytes (CTL) can control some viral infections and may be important in the control of lentiviruses, including human immunodeficiency virus type 1. Since there is limited evidence for an in vivo role of CTL in control of lentiviruses, dissection of immune mechanisms in animal lentiviral infections may provide needed information. Horses infected with equine infectious anemia virus (EIAV) a lentivirus, have acute plasma viremia which is terminated in immunocompetent horses. Viremic episodes may recur, but most horses ultimately control infection and become asymptomatic carriers. To begin dissection of the immune mechanisms involved in EIAV control, peripheral blood mononuclear cells (PBMC) from infected horses were evaluated for CTL to EIAV-infected cells. By using noninfected and EIAV-infected autologous equine kidney (EK) cells in 51Cr-release assays, EIAV-specific cytotoxic activity was detected in unstimulated PBMC from three infected horses. The EIAV-specific cytotoxic activity was major histocompatibility complex (MHC) restricted, as determined by assaying EIAV-infected heterologous EK targets, and was mediated by CD8+ T lymphocytes, as determined by depleting these cells by a panning procedure with an anti-CD8 monoclonal antibody. MHC-restricted CD8+ CTL in unstimulated PBMC from infected horses caused significant specific lysis of autologous EK cells infected with recombinant vaccinia viruses expressing EIAV genes, either env or gag plus 5' pol. The EIAV-specific MHC-restricted CD8+ CTL were detected in two EIAV-infected horses within a few days after plasma viremia occurred and were present after viremia was terminated. The detection of these immune effector cells in EIAV-infected horses permits further studies to determine their in vivo role.

Susceptibility of major histocompatibility complex (MHC) class I- and MHC class II-deficient mice to Cryptosporidium parvum infection

Major histocompatibility complex (MHC) class I-deficient and MHC class II-deficient mice lack functional CD8 T cells and CD4 T cells, respectively. These mice were evaluated for infection following oral administration of 10(7) Cryptosporidium parvum oocysts. MHC class II-deficient (but not MHC class I-deficient) mice dosed with C. parvum oocysts at 3 to 5 days of age remained infected 8 weeks postexposure. MHC class II-deficient mice exposed to C. parvum oocysts at 5 to 6 weeks of age were significantly more susceptible to infection than control mice (P < 0.0001).

Serum hypoxanthine and xanthine concentrations in horses heterozygous for combined immunodeficiency

SUMMARY

A group of diseases termed combined immunodeficiency (CID) results in a severe form of immunodeficiency. While CID in humans has two genetics bases, in Arabian it is inherited in an autosomal recessive manner. Kettler et al. (1989) determined that uric acid was significantly (p < .001) greater in the serum of carrier Arabian horses than in non-carrier horses. The current study measured serum levels of hypoxanthine and xanthine two other products of this pathway. There were no significant differences (p > 0.05) between carrier and non-carrier horse's serum levels of hypoxanthine or xanthine. These data, combined with our previous ones suggest that an enzymatic lesion in the purine salvage pathway may occur at the urate oxidase step. ZUSAMMENFASSUNG: Serum-Hypoxanthin- und -Xanthin-Spiegel in Pferden mit Heterozygotie für kombinierte Immundefizienz Kombinierte Immundefizienz (CID), die zu einer schweren Krankheit führt, hat beim Menschen zwei genetische Ursachen, wird aber bei Araberpferden autosomal rezessiv vererbt. Kettler u. Ma. (1989) fanden den Harnsäureserumspiegel in Überträgern signifikant höher als in freien Tieren. Hier wurden mit Hypoxanthin und Xanthin zwei andere Produkte des biochemischen Pfades bestimmt, jedoch keine statistisch signifikanten Unterschiede zu Nicht-Trägern der CID gefunden. Die Ergebnisse zusammen mit unseren früheren lassen vermuten, daß der Enzymmangel im Purinpfad auf der Harnsäureoxidationsstufe existiert.

Protective immunity to Haemonchus contortus induced by immunoaffinity isolated antigens that share a phylogenetically conserved carbohydrate gut surface epitope

Whole gut homogenates of the blood-sucking nematode Haemonchus contortus induce protective immunity in goats, and some of these gut Ag are conserved among related parasitic nematode species. To identify gut Ag that induce protective immunity and have phylogenetically conserved epitopes, mAb were made to gut-surface Ag of H. contortus. Forty-nine mAb reacted with microvilli of the parasite gut. Two of these mAb (42/10.6.1 and 42/53.3.5) were analyzed here. Both of the mAb bound to the microvillar surface of freshly isolated gut, and each mAb recognized carbohydrate epitopes, based on sensitivity to periodate oxidation. The 42/10.6.1 epitope occurred on at least 18 proteins in Western blots and in several H. contortus tissues. Proteins recognized by this mAb localized to membrane and excretory/secretory fractions of the worm. This epitope was also identified on the gut and other tissues and multiple proteins of related adult and larval nematodes, including larval Ancylostoma caninum and a mixed population of the free-living nematode Caenorhabditis elegans. In contrast, the 42/53.3.5 mAb bound to the gut surface and recognized proteins of 100 and 46 kDa from adult H. contortus gut. Four proteins of 100, 52, 46, and 30 kDa were isolated from the 42/53.3.5 immunoaffinity columns, and except for the 30-kDa protein, each was recognized by both the 42/10.6.1 and 42/53.3.5 mAb. Epitopes recognized by each mAb were distinct from one another and phosphorylcholine. When used to immunize goats, Ag isolated by both mAb induced protection that significantly (p < 0.05) reduced total worm counts after challenge infections compared with the control groups.

Protective immunity to Haemonchus contortus induced by immunoaffinity isolated antigens that share a phylogenetically conserved carbohydrate gut surface epitope

Whole gut homogenates of the blood-sucking nematode Haemonchus contortus induce protective immunity in goats, and some of these gut Ag are conserved among related parasitic nematode species. To identify gut Ag that induce protective immunity and have phylogenetically conserved epitopes, mAb were made to gut-surface Ag of H. contortus. Forty-nine mAb reacted with microvilli of the parasite gut. Two of these mAb (42/10.6.1 and 42/53.3.5) were analyzed here. Both of the mAb bound to the microvillar surface of freshly isolated gut, and each mAb recognized carbohydrate epitopes, based on sensitivity to periodate oxidation. The 42/10.6.1 epitope occurred on at least 18 proteins in Western blots and in several H. contortus tissues. Proteins recognized by this mAb localized to membrane and excretory/secretory fractions of the worm. This epitope was also identified on the gut and other tissues and multiple proteins of related adult and larval nematodes, including larval Ancylostoma caninum and a mixed population of the free-living nematode Caenorhabditis elegans. In contrast, the 42/53.3.5 mAb bound to the gut surface and recognized proteins of 100 and 46 kDa from adult H. contortus gut. Four proteins of 100, 52, 46, and 30 kDa were isolated from the 42/53.3.5 immunoaffinity columns, and except for the 30-kDa protein, each was recognized by both the 42/10.6.1 and 42/53.3.5 mAb. Epitopes recognized by each mAb were distinct from one another and phosphorylcholine. When used to immunize goats, Ag isolated by both mAb induced protection that significantly (p &lt; 0.05) reduced total worm counts after challenge infections compared with the control groups.

Effect of orally administered monoclonal antibody on persistent Cryptosporidium parvum infection in scid mice

Scid mice, persistently infected after exposure to 10(7) Cryptosporidium parvum oocysts, were treated daily for 14 to 17 days with 0.4 mg of monoclonal antibody (mAb) 17.41 administered by the oral route. Mice receiving mAb 17.41 shed significantly fewer (P < 0.005) C. parvum oocysts than scid mice receiving isotype control mAb. Intestinal (but not gastric) infectivity scores were also reduced for scid mice treated with mAb 17.41 (P < 0.01).

Antibody to a recombinant merozoite protein epitope identifies horses infected with Babesia equi

Horses infected with Babesia equi were previously identified by the presence of antibodies reactive with a merozoite surface protein epitope (D. P. Knowles, Jr., L. E. Perryman, L. S. Kappmeyer, and S. G. Hennager. J. Clin. Microbiol. 29:2056-2058, 1991). The antibodies were detected in a competitive inhibition enzyme-linked immunosorbent assay (CI ELISA) by using monoclonal antibody 36/133.97, which defines a protein epitope on the merozoite surface. The gene encoding this B. equi merozoite epitope was cloned and expressed in Escherichia coli. The recombinant merozoite protein, designated equi merozoite antigen 1 (EMA-1), was evaluated in the CI ELISA. Recombinant EMA-1 bound antibody from the sera of B. equi-infected horses from 18 countries. The antibody response to EMA-1 was then measured in horses experimentally infected with B. equi via transmission by the tick vector Boophilus microplus or by intravenous inoculation. Anti-EMA-1 antibody was detected 7 weeks post-tick exposure and remained, without reexposure to B. equi, for the 33 weeks of the evaluation period. The data indicate that recombinant EMA-1 can be used in the CI ELISA to detect horses infected with B. equi.

Surface epitope localization and gene structure of a Babesia bovis 44-kilodalton variable merozoite surface antigen

Variation of Babesia bovis merozoite surface antigens occurs among geographic strains of the parasite. In this and a concurrent report, we investigate this variation at the gene and protein level. Using a monoclonal antibody (mAb 23/70.174), B. bovis gene sequences were identified that encoded a surface epitope of a 44-kDa merozoite surface antigen (MSA-2). This epitope is variably expressed among geographic isolates of B. bovis. Here, we describe the MSA-2 protein gene sequence, localize this surface epitope to a repeated amino acid sequence, and investigate the genomic organization of the gene in B. bovis strains from Mexico and Australia. The predicted protein sequence had hydrophobic regions at its amino and carboxy termini consistent with a signal peptide and a membrane anchor via glycosylphosphatidyl inositol, respectively. The surface epitope recognized by mAb 23/70.174 was localized within a 24-amino acid sequence which is repeated twice in tandem. Six different EcoRI bands hybridized to the MSA-2 gene sequence with varying intensities in genomic Southern blots of the homologous strain. Two of these appear to be alleles of the MSA-2 gene. Whereas 5' and 3' sequences of the MSA-2 gene sequence were detected in an Australia strain of B. bovis, internal gene sequences encoding the surface epitope were not. The 3' sequences of the MSA-2 gene also had significant sequence similarity with the MSA-1 gene of the Mexico strain B. bovis and a gene from the previously described BabR locus. These data indicate that the MSA-2 protein gene belongs to the BabR locus which encodes variable merozoite surface antigens.