Hypoglobulinemia
Decreases in alpha and beta globulins are not significant. Decreased gamma globulins are seen when there is a deficiency of immunoglobulins (dependent on class of Ig involved and severity of the decrease). Radial immunodiffusion (RID) is the best method for pursuing these diagnoses.

Decreases in globulins of all fractions may be seen in protein-losing enteropathies, exudative dermatopathies, and hemorrhage. Concomitant loss of albumin in these conditions tends to maintain a normal A:G ratio with a low total protein.

Inherited hypogammaglobulinemia

A variety of inherited immunodeficient syndromes have been reported. Although some involve cell-mediated immunity (e.g. PSCID), they often have concurrent gamma globulin deficiencies due to impaired helper T cell function.
  • Primary severe combined immunodeficiency: This has been reported in Bassett hounds, Cardigan Welsh Corgis, Daschunds and Arabians (full and crosses). It is characterized by a lymphopenia, decreased IgM in a presuckle foal, absent IgM and IgA post-suckling. IgM, IgG and IgA are all low after 3 months of age as maternally-derived antibodies are degraded. Animals have thymic and lymph node atrophy and die at a young age (usually when maternal antibodies disappear) of opportunistic infections, e.g. Pneumocystis carinii, adenovirus, cryptosporidiosis.
  • Agammaglobulinemia: This has been reported in foals. They have no B cells and lack Igs by 3 months of age. T cell function is normal as are lymphocyte counts. They die of repeated infections, with a poor response to therapy, by 12-18 months of age.
  • IgM deficiency: Selective IgM deficiency has been reported in horses (Arabians, Paso Fino, quarterhorses and thoroughbreds) and Dobermans. Horses usually die of fatal pneumonia, arthritis and enteritis. Dogs usually have no clinical signs as long as IgG and IgA levels are normal.
  • IgA deficiency: This has been reported in various dog breeds, including Sharpeis, Beagles, Airedale terriers, and German Shepherd Dogs. They suffer from recurrent infections involving the urinary tract, respiratory tract, and skin.
  • Transient hypogammaglobulinemia: This has been reported in Arabian horses and dogs. They have a delayed onset of post-natal immunoglobulin synthesis and are susceptible to adenoviral and bacterial infections.
Acquired immunodeficiencies

These are, by far, more common than inherited immunodeficiencies.
  • Failure of passive transfer (FPT): Animals are dependent upon ingestion of colostrum for passive immunity as immunoglobulins do not cross the placenta as they do in human beings. FPT results when neonates fail to suckle or if dams leak colostrum pre-parturition. For diagnosis of FPT, determination of IgG is recommended within 24 to 48 hours of birth. Rapid ELISA assays are available, however RID is more accurate (but slow - a minimum of 24 hours is required). In calves, zinc sulfate turbidity, glutaraldehyde coagulation and sodium sulfite precipitation tests can be used, but are not as accurate as direct measurement of IgG.
    For foals, the following guidelines are used:

    Complete FPT: IgG < 200 mg/dL
    Partial FPT: IgG = 200-800 mg/dL
    Passive transfer: > 800 mg/dL.

    For llamas, use the following:

    Complete FPT: IgG < 800 mg/dL
    Passive transfer: IgG > 800 mg/dL

    For calves, guidelines are:

    Complete FPT: IgG < 1200 mg/dL
    Passive transfer: IgG > 1200 mg/dL

    Note that for calves, a GGT value of < 200 U/L or a total protein concentration of < 4.2 g/L have a sensitivity of 80% for diagnosis of FPT (GGT is high in the colostrum of cattle, sheep, goats, dogs and cats [but not horses]).
  • Infectious diseases
    1) Viruses: Feline leukemia virus and feline immunodeficiency virus are known causes for acquired immunodeficiencies in cats. Canine distemper virus causes immunodeficiency in dogs. Bovine viral diarrhea causes immunodeficiency in cattle and Aleutian mink disease virus (a parvovirus) causes immunosuppression in ferrets.
    2) Parasites: Toxoplasmosis and Theileria cause immunodeficiency. Generalized infection with Demodex canis is often found in immunodeficient dogs, however it may be a result of immunodeficiency and not its cause. Eperythrozoon wenyonii infection in cattle is associated with reduced humoral immunity.
    3) Johne's disease causes decreased T cell function.
  • Neoplasia: Lymphoma in cattle and horses is associated with immunosuppression. Very low IgM levels are often observed in horses with lymphoma and can be a valuable non-invasive tumor marker if there is a high clinical index of suspicion for lymphoma.Eperythrozoon in a llama
  • Idiopathic: Idiopathic immunodeficiency has been reported in young llamas with failure to gain weight, ill-thrift and recurrent infections. Many of these llamas have concurrent Eperythrozoon infections (shown in the photomicrograph above).

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