Development and validation of an improved enzyme-linked immunosorbent assay for the detection of thyroglobulin autoantibodies in canine serum samples

Assessment of the likelihood of hypothyroidism in dogs diagnosed with and treated for hypothyroidism at primary care practices: 102 cases (2016-2021)

BACKGROUND

There is a possibility that an incorrect diagnosis of hypothyroidism could be made in euthyroid dogs, and the prevalence of hypothyroidism in the dog population remains unknown.

OBJECTIVES

To retrospectively assess the percentage of dogs diagnosed with, and treated for, hypothyroidism at first opinion practice which are likely to be hypothyroid and require levothyroxine supplementation.

ANIMALS

One hundred two client-owned dogs were included in this study.

MATERIALS AND METHODS

The computerized databases of 7 first opinion practices were searched to identify dogs treated with levothyroxine supplementation. Three European College of Veterinary Internal Medicine-Companian Animals (ECVIM-CA) diplomates independently assigned 1 of 4 clinical assessments to each case as follows: confirmed or likely hypothyroid, hypothyroidism suspected but not confirmed, hypothyroidism considered unlikely, and no reason to suspect hypothyroidism. They commented as to whether or not they thought levothyroxine supplementation was appropriate.

RESULTS

The clinical assessments of "confirmed or likely hypothyroid"; "Hypothyroidism suspected but not confirmed"; "Hypothyroidism considered unlikely"; and "No reason to suspect hypothyroidism" was assigned respectively by Clinician 1 to 38.2%, 5.9%, 3.9%, and 52% of cases, by Clinician 2 to 48%, 22.6%, 22.6%, 6.9% of cases, and by Clinician 3 to 55.9%, 11.8%, 13.7% and 18.6%. Clinician 1, Clinician 2, and Clinician 3 considered levothyroxine supplementation not indicated in 58.8%, 52.9%, and 45.1% of cases, respectively.

CONCLUSION

These results support the concern that hypothyroidism might be overly and incorrectly diagnosed in first opinion practice, and that thyroid function testing should be performed only in those dogs with a high pretest probability of the disease.

A scoping review of autoantibodies as biomarkers for canine autoimmune disease

Background

Autoantibody biomarkers are valuable tools used to diagnose and manage autoimmune diseases in dogs. However, prior publications have raised concerns over a lack of standardization and sufficient validation for the use of biomarkers in veterinary medicine.

Objectives

Systematically compile primary research on autoantibody biomarkers for autoimmune disease in dogs, summarize their methodological features, and evaluate their quality; synthesize data supporting their use into a resource for veterinarians and researchers.

Animals

Not used.

Methods

Five indices were searched to identify studies for evaluation: PubMed, CAB Abstracts, Web of Science, Agricola, and SCOPUS. Two independent reviewers (AET and ELC) screened titles and abstracts for exclusion criteria followed by full‐text review of remaining articles. Relevant studies were classified based on study objectives (biomarker, epitope, technique). Data on study characteristics and outcomes were synthesized in independent data tables for each classification.

Results

Ninety‐two studies qualified for final analysis (n = 49 biomarker, n = 9 epitope, and n = 34 technique studies). A high degree of heterogeneity in study characteristics and outcomes reporting was observed. Opportunities to strengthen future studies could include: (1) routine use of negative controls, (2) power analyses to inform sample sizes, (3) statistical analyses when appropriate, and (4) multiple detection techniques to confirm results.

Conclusions

These findings provide a resource that will allow veterinary clinicians to efficiently evaluate the evidence supporting the use of autoantibody biomarkers, along with the varied methodological approaches used in their development.

Serum Antibodies Against the Oncogenic Merkel Cell Polyomavirus Detected by an Innovative Immunological Assay With Mimotopes in Healthy Subjects

Merkel cell polyomavirus (MCPyV), a small DNA tumor virus, has been detected in Merkel cell carcinoma (MCC) and in normal tissues. Since MCPyV infection occurs in both MCC-affected patients and healthy subjects (HS), innovative immunoassays for detecting antibodies (abs) against MCPyV are required. Herein, sera from HS were analyzed with a novel indirect ELISA using two synthetic peptides mimicking MCPyV capsid protein epitopes of VP1 and VP2. Synthetic peptides were designed to recognize IgGs against MCPyV VP mimotopes using a computer-assisted approach. The assay was set up evaluating its performance in detecting IgGs anti-MCPyV on MCPyV-positive (n=65) and -negative (n=67) control sera. Then, the ELISA was extended to sera (n=548) from HS aged 18-65 yrs old. Age-specific MCPyV-seroprevalence was investigated. Performance evaluation indicated that the assay showed 80% sensitivity, 91% specificity and 83.9% accuracy, with positive and negative predictive values of 94.3% and 71%, respectively. The ratio expected/obtained data agreement was 86%, with a Cohen's kappa of 0.72. Receiver-operating characteristic (ROC) curves analysis indicated that the areas under the curves (AUCs) for the two peptides were 0.82 and 0.74, respectively. Intra-/inter-run variations were below 9%. The overall prevalence of serum IgGs anti-MCPyV in HS was 62.9% (345/548). Age-specific MCPyV-seroprevalence was 63.1% (82/130), 56.7% (68/120), 64.5% (91/141), and 66.2% (104/157) in HS aged 18-30, 31-40, 41-50 and 51-65 yrs old, respectively (p>0.05). Performance evaluation suggests that our indirect ELISA is reliable in detecting IgGs anti-MCPyV. Our immunological data indicate that MCPyV infection occurs asymptomatically, at a relatively high prevalence, in humans.

Whole-genome genotyping and resequencing reveal the association of a deletion in the complex interferon alpha gene cluster with hypothyroidism in dogs

Background

Hypothyroidism is a common complex endocrinopathy that typically has an autoimmune etiology, and it affects both humans and dogs. Genetic and environmental factors are both known to play important roles in the disease development. In this study, we sought to identify the genetic risk factors potentially involved in the susceptibility to the disease in the high-risk Giant Schnauzer dog breed.

Results

By employing genome-wide association followed by fine-mapping (top variant p-value = 5.7 × 10^− 6), integrated with whole-genome resequencing and copy number variation analysis, we detected a ~ 8.9 kbp deletion strongly associated (p-value = 0.0001) with protection against development of hypothyroidism. The deletion is located between two predicted Interferon alpha (IFNA) genes and it may eliminate functional elements potentially involved in the transcriptional regulation of these genes. Remarkably, type I IFNs have been extensively associated to human autoimmune hypothyroidism and general autoimmunity. Nonetheless, the extreme genomic complexity of the associated region on CFA11 warrants further long-read sequencing and annotation efforts in order to ascribe functions to the identified deletion and to characterize the canine IFNA gene cluster in more detail.

Conclusions

Our results expand the current knowledge on genetic determinants of canine hypothyroidism by revealing a significant link with the human counterpart disease, potentially translating into better diagnostic tools across species, and may contribute to improved canine breeding strategies.

Increased genetic risk or protection for canine autoimmune lymphocytic thyroiditis in Giant Schnauzers depends on DLA class II genotype

Dogs represent an excellent comparative model for autoimmune thyroiditis as several dog breeds develop canine lymphocytic thyroiditis (CLT), which is clinically similar to Hashimoto's thyroiditis in human. We obtained evidence that dog leukocyte antigen (DLA) class II genotype function as either genetic risk factor that predisposes for CLT or as protective factor against the disease. Genetic diversity at their DLA-DRB1, -DQA1, and -DQB1 loci were defined and potential association to major histocompatibility complex II haplotypes and alleles was analyzed. Giant Schnauzers carrying the DLA-DRB1*01201/DQA1*00101/DQB1*00201 haplotype showed an increased risk (odds ratio of 6.5) for developing CLT. The same risk haplotype has, to date, been observed in three different breeds affected by this disease, Giant Schnauzer, Dobermann, and Labrador Retriever, indicating that it is a common genetic risk factor in a variety of breeds affected by this disease. Importantly, protection for development of the disease was found in dogs carrying the DLA-DRB1*01301/DQA1*00301/DQB1*00501 haplotype (odds ratio of 0.3).

Etiopathologic Findings of Canine Hypothyroidism

The causes of canine hypothyroidism are varied, but most cases result from irreversible acquired thyroid pathologic changes and only a small proportion arise from congenital anomalies of the thyroid gland or pituitary. Of primary thyroid failure, at least half is the result of immune-mediated thyroiditis. Recent research has focused on the genetics and immunology of canine thyroid disease, adding to what is known from experimental and human studies. Epidemiologic and diagnostic laboratory studies continue to provide information on contributing factors and raise questions for future research directions. Serum antibodies against thyroid components are common in thyroid pathologic conditions and dysfunction, and understanding their properties and frequency is important in the interpretation of thyroid diagnostic test results.

Proliferative Responses to Canine Thyroglobulin of Peripheral Blood Mononuclear Cells from Hypothyroid Dogs

The immune responses of hypothyroid dogs to canine thyroglobulin (cTg) were evaluated for the proliferative ability of peripheral blood mononuclear cells (PBMC). PBMC from three hypothyroid dogs with high titers of thyroglobulin autoantibody (TgAA) and 3 clinically normal dogs were cultured with 5, 10, or 20 microg/ml of cTg for 72 hr. The proliferative responses of the cells were determined by the level of incorporated BrdU. The numbers of cells expressing Thy-1, CD4, CD8 and IgG in the PBMC were counted by the immunofluorescence method. Proliferative responses to cTg were observed in the cells from hypothyroid dogs. The number of cells expressing IgG and CD8 in the hypothyroid dogs tended to be high compared with the clinically normal dogs. The CD4+ cells in cultures from hypothyroid dogs increased depending upon the amount of cTg. There was a significant (P<0.05) positive correlation between the number of CD4+ cells and the concentration of cTg in the cultures from hypothyroid dogs. These findings suggest a possible relationship between canine hypothyroidism and cellular immunity. Loss of self tolerance to thyroid antigens in CD4+ T cells may play an important role in the development of canine hypothyroidism.

Standardization and validation of an alkaline phosphatase-linked immunoassay to quantify a plant-derived antibody directed against the hepatitis B virus surface antigen

Immunopurification is one of the most effective chromatography steps to purify the hepatitis B surface antigen, which have successfully been used as an active pharmaceutical ingredient of hepatitis B vaccines. Plant-derived antibodies could be an appropriated ligand for such purposes because plants are the most cost-effective production systems and have the additional advantage that plant viruses cannot infect humans. In this work, a polyclonal antibody alkaline phosphatase-linked immunoassay was standardized and validated to quantify a plant-derived antibody directed against the HBsAg. The validation of an immunoassay to quantify plantibodies is a relatively complex task due to the complexity of the plant extract, the low level of expression of this molecule, and the potential interferences of endogenous peroxidases contributed by plants. These results allow estimating the plant-derived antibody concentration up to 3.81 ng/mL with high specificity, precision, and repeatability. The working range of the standard curve was between 3.81 and 60 ng/mL, and the intra- and inter-variation coefficients were between 10% and 20% in a production process's sample dependent way. This enzyme-linked immunosorbent assay is considered valuable to improve the design of the purification process and also to obtain a better estimation of the antibody expression level and process's recovery.

Tryptic peptides of canine thyroglobulin reactive with sera of patients with canine hypothyroidism caused by autoimmune thyroiditis

Canine thyroglobulin (cTg) was treated with trypsin at a ratio of trypsin to cTg of 1:100 (w/w). Tryptic peptides of cTg were analysed by Western immunoblotting for their reactivity to serum thyroglobulin autoantibodies (TgAA) from patients with TgAA-positive hypothyroidism and normal individuals. The sera of patients with TgAA-positive hypothyroidism reacted with several peptides: 43, 32.5 and 31 kDa; the sera of normal individuals did not bind these tryptic peptides. Some of the TgAA-positive sera of patients reacted with 25 kDa peptide in addition to three tryptic peptides above. This experiment was the first report about antigenic epitopes of cTg. These small tryptic peptides recognized by TgAA may be related with the induction of TgAA and may be useful as markers for autoimmune thyroid diseases in dog.

Endocrine diseases in dogs and cats: similarities and differences with endocrine diseases in humans

Over several millennia, humans have created hundreds of dog and cat breeds by selective breeding, including fixation of mutant genes. The domestic dog is unique in the extent of its variation in height, weight and shape as well as its behavior. It is primarily the relatively long persistence of high levels of growth hormone (GH) release at a young age that accounts for the large body size in giant breeds of dogs. Several of the endocrine diseases of humans are also known to occur as similar entities in dogs and cats. With some variations, this is true for conditions such as diabetes mellitus and the hypofunction syndromes of the thyroid and adrenal cortex. Also, the hyperfunction syndromes of hypercortisolism and hyperparathyroidism in dogs and cats have many similarities with their human counterparts. The exception seems to be Graves' disease. This condition, which is due to production of thyroid-stimulating hormone (TSH)-receptor antibodies, has not been observed in dogs and cats. The very common form of hyperthyroidism in cats is due to toxic adenomas. In the 1980s it was discovered that in dogs exogenous progestins and endogenous progesterone can induce GH excess. This GH excess originates form the mammary gland and may give rise to acromegaly and insulin resistance. GH production by the mammary gland is not unique to the dog. It has become clear that cats and humans also express the GH gene in the mammary gland. There is increasing evidence that this locally produced GH not only plays a role in the morphologic changes of the mammary gland associated with the ovarian cycle and gestation, but that it is also involved in the development of breast cancer. In dogs, induction of mammary GH production by progestin administration allows for treatment of GH deficiency.

Determination of autoantibodies to thyroglobulin, thyroxine and triiodothyronine in canine serum

Enzyme immunoassays (EIAs) for the determination of autoanti-bodies (AA) to thyroid antigens in canine serum were developed. Streptavidin (SA) was immobilized as capture molecule on microtitreplates (MTP). Thyroglobulin (Tg) purified from canine thyroids and the thyroid hormones thyroxine and triiodothyronine (T3 and T4) were conjugated to biotin labelling reagents and attached to the MTP over the SA-biotin bridge. Bound AA were detected with anti-dog-immunoglobulin G (IgG) labelled with horseradish peroxidase. Serum samples from dogs which were allotted to four groups were analysed: A (n = 31), biochemical evidence of hypothyroidism; B (n = 76), clinical signs of hypothyroidism; C (n = 47), euthyroid with non-thyroidal disease; D (n = 186), clinically healthy. The validity of the assays was tested with two different methods. After thiophilic absorption chromatography of positive sera, a positive reaction in the EIA was only detected in those fractions which coeluted with the canine IgG standard. Furthermore, the positive reaction was blocked by the addition of the corresponding antigen. In 55% of the hypothyroid dogs AA to Tg and/or T3 and T4, respectively, were found (up to a titre of 1 : 1600). In group B 34% of the dogs were diagnosed positive, but the titre was lower (up to 1 : 400). In the groups C and D the number of dogs with AA and their titre was significantly lower. Two different methods for distinguishing positive and negative test results were compared in order to increase the specificity of the tests without decreasing the sensitivity. The EIAs are precise and based on high agreement with previous reported assays able to discriminate dogs with thyroiditis from healthy ones. These assays represent a good alternative to the isotope assays generally used for the analysis of AA to T4 and T3.

Recognition Pattern of Thyroglobulin Autoantibody from Hypothyroid Dogs to Tryptic Peptides of Canine Thyroglobulin

Circulating thyroglobulin autoantibody (TgAA) was analyzed using the Western immunoblot for determination of the dominant epitopes recognized by TgAA on tryptic peptides of canine thyroglobulin (cTg) in hypothyroid dogs. TgAA was measured in hypothyroid dogs, non-hypothyroid dogs with skin diseases and clinically normal dogs. Five of the 7 hypothyroid dogs, 1 of the 8 dogs with skin diseases and 1 of the 4 normal dogs were positive for TgAA. Four of the 5 TgAA-positive hypothyroid dogs were Golden Retrievers, and 3 of them showed high antibody titers. The sera of TgAA positive-dogs reacted to several peptides, and their patterns varied from sample to sample. Sera from 3 dogs with high titers of TgAA reacted broadly to high molecular weight peptides ranging from 45 to 90 kDa. These Western immunoblot patterns of the sera were disappeared after pretreatment with sufficient amount of intact cTg. All serum samples of both TgAA positive dogs and negative controls reacted to low molecular weight peptides ranging from 15 to 20 kDa. These immunoblot patterns of the sera were not disappeared even after pretreatment with sufficient amount of intact cTg. These findings show the possibility that the epitopes recognized by TgAA depend upon individual dogs with hypothyroidism and these autoantibodies recognize conformational epitopes on the cTg molecule.

Evaluation of antithyroglobulin antibodies after routine vaccination in pet and research dogs

OBJECTIVE

To determine whether routine vaccination induces antibodies against bovine thyroglobulin and autoantibodies against canine thyroglobulin in dogs.

DESIGN

Prospective study.

ANIMALS

20 healthy research Beagles and 16 healthy pet dogs.

PROCEDURE

For the research Beagles, 5 dogs were vaccinated with a multivalent vaccine and a rabies vaccine, 5 dogs received only the multivalent vaccine, 5 dogs received only the rabies vaccine, and 5 dogs were unvaccinated controls. The multivalent vaccine was administered at 8, 10, 12, 16, 20, 26, and 52 weeks of age and every 6 months thereafter. The rabies vaccine was administered at 16 and 52 weeks of age and then once per year. Blood was collected from all dogs at 8, 16, and 26 weeks of age and then 4 times yearly. Assays for antibodies directed against bovine and canine thyroglobulin were performed prior to and 2 weeks after each yearly vaccination. For the pet dogs, blood was collected prior to and 2 weeks after 1 vaccination.

RESULTS

In the research Beagles, there was a significant increase in anti-bovine thyroglobulin antibodies in all vaccinated dogs, compared with control dogs. There was a significant increase in anti-canine thyroglobulin antibodies in the 2 groups of dogs that received the rabies vaccine but not in the group that received the multivalent vaccine alone. In the pet dogs, there was a significant increase in anti-canine thyroglobulin antibodies after vaccination but no significant change in anti-bovine thyroglobulin antibodies.

CONCLUSIONS AND CLINICAL RELEVANCE

Recent vaccination may result in increased anti-canine thyroglobulin antibodies. Whether these antibodies have a deleterious effect on canine thyroid function is unknown.

Biological variation of canine serum thyrotropin (TSH) concentration

The aim of the present study was to estimate the between-dog, within-dog and analytical components of variance for serum thyrotropin (TSH) in healthy dogs, and to use these components of variance to 1) estimate the critical difference for significance between serial results; 2) assess the utility of the conventional population-based reference interval; 3) set a desirable performance standard for analytical imprecision; and 4) estimate the number of samples required for determination of the true mean value for an individual dog. Using the Immulite test system, TSH was measured in serum samples collected weekly for five weeks from eight clinically healthy dogs. Results were subjected to nested analysis of variance. Between-dog variation was 43.6%, within-dog variation was 13.6%, analytical variation was 8.8%, the one-sided critical difference was 37.8%, the index of individuality was 0.4, the maximum allowable analytical imprecision was 6.8%, and the number of samples required to determine the true mean value in a single dog was 40. In practical terms, the present study indicated that the analytical imprecision of canine serum TSH measurement should be < 7%, and that comparing a single serum TSH measurement from an individual dog to the conventional population-based reference range may be too insensitive to detect small but important changes in the serum TSH level of that particular dog. In addition, when treating a hypothyroid dog, serum TSH, measured on a weekly basis, should decrease by at least one-third before any effect of exogenous thyroxine supplementation can be said to have influenced the serum TSH level.

Lymphocytic thyroiditis

Lymphocytic thyroiditis is a common canine condition that can lead to functional hypothyroidism. It is associated with more than 50% of cases of canine hypothyroidism. Evidence in human beings and experimental situations suggests that it is a disease of defective immunoregulation, but specific investigation of the molecular pathogenesis of the naturally occurring disease in dogs has not yet been carried out. The condition is heritable in those breeds that have been studied, and progression to hypothyroidism, if it occurs, can be slow. Factors that influence the progression from subclinical thyroiditis to hypothyroidism in dogs are still to be identified, but excessive iodine intake is an important factor in other species.