INTRODUCTION

Primary, congenital, inherited immunodeficiency disorders are uncommon in the dog. By contrast, immunodeficiency in adult animals secondary to a wide range of defined causes (e.g., age, drug therapy, chronic neoplastic or infectious disease) is relatively common.

The primary immunodeficiencies reflect a developmental block at one or more levels of maturation of the immune or haemopoietic systems. A defect at the level of stem cells will give rise to a more profound clinical syndrome than for example, a selective inability to produce immunoglobulin of a single class. Primary immunodeficiency will often be recognised within litters of animals after the protective effect of maternal immunoglobulin has been lost (12-15 weeks of age). Most canine immunodeficiencies are breed-related. The occurrence of chronic recurrent infections, infection at multiple sites, infection with environmental saprophytes or illness after live viral vaccination in susceptible animals of this age should trigger investigation of possible immunodeficiency.

DIAGNOSIS OF IMMUNODEFICIENCY

The diagnosis of immunodeficiency should progress through stages of complexity. Basic characterisation of the problem may include routine haematological examination (specifically assessing leucocytes), assessment of serum proteins, culture and identification of pathogens, and full necropsy examination of any affected animals (i.e., within a litter) that die during the investigation. The necropsy should pay specific attention to lymphoid organs and histological examination of thymus, spleen, lymph node, bone marrow and gut should be performed if possible.

The ideal secondary stage of investigation would include full screening of the quantity and functional capacity of the various components of the immune system, including the humoral, cell-mediated and phagocytic arms¹. In theory, a very detailed examination of the canine immune system is now possible and a wide range of techniques has been validated in a research setting. In practice, such tests are rarely available on a commercial basis to veterinarians in practice. It is generally possible to have the serum concentration of the major immunoglobulin classes (IgG, IgM and IgA) assessed in the dog, and commercial laboratories have increasing access to assessment of blood lymphocyte subpopulations (e.g., CD4 and CD8 T lymphocytes, CD21 B lymphocytes) by flow cytometry. Unfortunately, the more relevant tests of lymphocyte proliferative response and neutrophil/macrophage chemotaxis, phagocytosis and killing assays are less accessible. In three canine immunodeficiencies (C3 deficiency, X-linked severe combined immunodeficiency, canine leucocyte adhesion deficiency), the precise molecular defect has been characterised, and a commercially available molecular test is available for confirmation of the CLAD mutation.

IMMUNODEFICIENCY DISEASES IN THE DOG

The major primary immunodeficiency diseases of the dog are summarised below. Some of these reports refer to limited episodes in specific groups of dogs kept for research purposes, and the defects are not widespread in the breeds. In many cases the immunological defects and their mode of transmission have been poorly characterised.

The most widely recognised canine (and human) immunodeficiency is selective deficiency of immunoglobulin A (IgA). In both species this appears not to be an absolute lack of IgA due to a mutation in the gene encoding the immunoglobulin alpha chain, but a relative deficiency in concentration of this immunoglobulin in serum or at mucosal surfaces. IgA deficiency has been reported in the Shar pei, beagle, English cocker spaniel, Irish wolfhound and German shepherd dog, and may be part of a more complex deficiency state in Rottweilers, Weimaraners, English bull terriers and miniature dachshunds. As in humans, canine IgA deficiency has been clinically associated with a range of infectious, inflammatory, allergic and autoimmune diseases.

Most research into canine IgA deficiency has been undertaken in dogs of the German shepherd breed. Our own investigations of German shepherds with inflammatory enteropathies have shown that these dogs may have low concentrations of IgA in the intestinal lumen despite having normal numbers of IgA secreting plasma cells in the intestinal mucosa, and normal serum concentrations of this molecule². There are no defects in the ability of German shepherd dogs to express the IgA alpha chain gene, or the genes encoding molecules involved in the transport of IgA across the intestinal epithelial barrier³. Current molecular studies have identified several genetic variants of canine IgA, and selective usage of particular variants might occur in German shepherd dogs.

Recent studies of Irish wolfhounds with chronic recurrent rhinitis and/or bronchopneumonia have also suggested a role for IgA deficiency in the pathogenesis of the disorder. Affected dogs may have low serum IgA, but the concentration of IgA within bronchoalveolar lavage fluid is normal or raised⁴. There are also lymphocyte subset abnormalities documented within this lavage fluid, and poor lymphocyte response to mitogenic stimulation is described⁵.

English bull terriers with 'lethal acrodermatitis' have been shown to have selective deficiency of serum IgA concentration. In addition, affected dogs have poor responsiveness of T lymphocytes to mitogen stimulation⁶.

Deficiency of IgG has been documented in Weimaraners, cavalier King Charles spaniels (CKCS) and as part of a more complex immunodeficiency in Rottweilers and miniature dachshunds. Young, related Weimaraner dogs are reported with multisystemic inflammatory and infectious disease from the age of approximately 15 weeks^7,8. These dogs most consistently have subnormal concentration of serum IgG (sometimes with low IgM and IgA) and neutrophil functional defects have also been reported⁹. Vaccination is thought to act as a trigger factor in this complex disease syndrome¹⁰. Young CKCS and miniature dachshunds with pneumonia caused by Pneumocystis carini also have subnormal serum IgG, and lymphocyte function defects have also been documented in affected miniature dachshunds¹.

Dogs of the Rottweiler breed have long been suggested to have an immunodeficiency syndrome, dating from their susceptibility to parvoviral infection and suggested poor vaccine responses. A litter of Rottweiler pups with subnormal serum immunoglobulin concentrations and abnormalities in lymphoid tissue has been described¹², and another dog of this breed has been reported with deficiency in granulocyte-colony stimulating factor¹³.

Only a single complement deficiency has been described in the dog. A research colony of Brittany spaniels has been well documented in the literature and the underlying molecular defect is described.

In addition to possible neutrophil dysfunction in Weimaraners, abnormal neutrophil function was once documented in Doberman pinschers with respiratory disease. A number of studies have examined the syndrome of cyclic haematopoiesis in grey collie dogs, and these animals have proven useful as an experimental model for therapeutic approaches to immunodeficiency (see below). Another well-defined immunodeficiency affecting neutrophils is the CLAD (canine leukocyte adhesion deficiency) mutation in Irish (red, or red and white) setters. The neutrophils of affected dogs fail to express the adhesion molecules CD11b and CD18, so despite massive blood neutrophilia these cells cannot egress into tissues to fight infection¹⁴. A persistent neutropenia was described in border collie dogs in New Zealand in which there was apparent failure of release of neutrophils from the bone marrow. The Pelger-Huët anomaly, characterised by hyposegmentation of granulocyte nuclei, has been described in American foxhounds, cocker spaniels, Boston terriers and basenjis.

The best-defined canine lymphoid immunodeficiency is X-linked severe combined immunodeficiency (X-SCID) described in the basset hound and corgi¹⁵. Affected dogs have been studied in research colonies as a model for the equivalent disease in humans. Canine X-SCID involves a mutation in the common chain of receptor molecules for the cytokines IL-2, IL-4, IL-7, IL-15 and IL-19. More recently, a non-X-linked form of SCID has been described in a colony of Jack Russell terriers¹⁶. The genetic defect in these dogs relates to defective DNA-dependent protein kinase that is responsible for molecular recombination giving rise to functional T and B lymphocyte receptors. This form of SCID is similar to that that has long been recognised in Arabian horses. Mexican hairless dogs have been described as having subnormal immunoglobulin concentration, impaired delayed hypersensitivity response and depletion of lymphoid tissue. The association of hairlessness and immunodeficiency is well recognised in inbred laboratory strains of 'nude' athymic rats and mice.

THERAPEUTIC APPROACHES TO IMMUNODEFICIENCY

Therapeutic options for animals with primary immunodeficiency disease are limited. Most cases are fatal, but symptomatic and antimicrobial therapy can sometimes prolong life for restricted periods. Crude immunomodulatory drugs are sometimes administered, but the effects of these are poorly documented. A range of experimental therapies have been attempted in dogs with cyclic haematopoiesis, particularly recombinant cytokine therapy (e.g., canine granulocyte colony stimulating factor and stem cell factor), and bone marrow transplantation. Bone marrow transplantation has also been successfully used to experimentally treat dogs with X-SCID and CLAD¹⁷. Such canine studies are generally performed from the perspective of using the dog as a model for developing therapy for the counterpart human diseases. The availability of these canine models will in future permit the testing of gene replacement therapy for immunodeficiency. A preliminary study has shown that administration of the canine G-CSF gene in a lentivirus vector resulted in elevation of blood neutrophils in a grey collie with cyclic neutropenia for over 17 months¹⁸.

Of more relevance and importance is the elimination of such traits from breeding stock, by not breeding from affected animals and by genetic screening of breeding pairs where molecular testing exists. This approach has been very successful for the CLAD mutation in Irish setters, where widespread testing and the collaboration of the breed society have meant that the goal of eliminating this trait from the breed is becoming achievable¹⁹.

References

1.  Day MJ. Immunodeficiency disease. In: Clinical Immunology of the Dog and Cat. MJ Day. 1999. Manson publishing, London. pp. 197-215.

2.  German AJ, Hall EJ and Day MJ. Relative deficiency in IgA production by duodenal explants from German shepherd dogs with small intestinal disease. Vet Immunol Immunopathol 2000; 76: 25-43.

3.  Peters IR, Helps CR, Batt RM, Day MJ and Hall EJ. Quantitative real-time RT-PCR measurement of mRNA encoding-chain, pIgR and J-chain from canine duodenal mucosa. J Immunol Methods 2003; 275: 213-222.

4.  Clercx C, Reichler I, Peeters D, McEntee K, German A, Dubois J, Schynts F, Scaaf-Lafontaine N, Willems T, Jorissen M, Day MJ. Rhinitis/bronchopneumonia syndrome in Irish Wolfhounds. J Vet Intern Med 2003; 17: 843-849.

5.  Leisewitz AL, Spencer JA, Jacobson LS, Schroeder H. Suspected primary immunodeficiency syndrome in three related Irish wolfhounds. J Small Anim Pract 1997; 38: 209-212.

6.  McEwan NA, Huang HP and Mellor DJ. Immunoglobulin levels in bull terriers suffering from lethal acrodermatitis. Vet Immunol Immunopathol 2003; 96: 235-238.

7.  Day MJ, Power C, Oleshko J, Rose M. Low serum immunoglobulin concentrations in related Weimaraner dogs. J Small Anim Pract 1997; 38: 311-315.

8.  Abeles V, Harrus S, Angles JM, et al. Hypertrophic osteodystrophy in six Weimaraner puppies associated with systemic signs. Vet Rec 1999; 145: 130-134.

9.  Foale RD, Herrtage ME and Day MJ. Retrospective study of 25 young Weimaraners with low serum immunoglobulin concentrations and inflammatory disease. Vet Rec 2003; 153: 553-558.

10. Harrus S, Waner T, Aizenberg I et al. Development of hypertrophic osteodystrophy and antibody response in a litter of vaccinated Weimaraner puppies. J Sm Anim Pract 2002; 43: 27-31.

11. Lobetti RG. Pneumocystis carinii infection in miniature dachshunds. Comp Cont Educ Pract Vet 2001; 23: 320-324.

12. Day MJ. Possible immunodeficiency in related Rottweiler dogs. J Small Anim Pract 1999; 40: 561-568.

13. Lanevschi A, Daminet S, Niemeyer GP, Lothrop CD. Granulocyte colony-stimulating factor deficiency in a Rottweiler with chronic idiopathic neutropenia. J Vet Intern Med 1999; 13: 72-75.

14. Trowald-Wigh G, Ekman S, Hansson K, et al. Clinical, radiological and pathological features of 12 Irish setters with canine leucocyte adhesion deficiency. J Small Anim Pract 2000; 41: 211-217.

15. Felsburg PJ, Hartnett BJ, Henthorn PS, et al. Canine X-linked severe combined immunodeficiency. Vet Immunol Immunopathol 1999; 69: 127-135.

16. Meek K, Kienker L, Dallas C et al. SCID in Jack Russell terriers: a new animal model of DNA-PKcs deficiency. J Immunol 2001; 167: 2142-2150.

17. Creevy KE, Bauer TR, Tuschong LM et al. Mixed chimeric hematopoietic stem cell transplant reverses the disease phenotype in canine leukocyte adhesion deficiency. Vet Immunol Immunopathol 2003; 95: 113-121.

18. Yanay O, Barry SC, Katen LJ et al. Treatment of canine cyclic neutropenia by lentivirus-mediated G-CSF delivery. Blood 2003; 102: 2046-2052.

19. Jobling AJ, Ryan J and Augusteyn RC. The frequency of the canine leukocyte adhesion deficiency (CLAD) allele within the Irish setter population of Australia. Aust Vet J 2003; 81: 763-765.