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Staphylococcal protein A binding to canine IgG and IgM
M A Scott1, J M Davis, K A Schwartz
1Department of Pathology, Michigan State University, East Lansing, USA. scott@vmdl.missouri.edu
Veterinary Immunology and Immunopathology
|February 27, 1998
Summary
Staphylococcal protein A (SpA) shows incomplete binding to canine IgG and IgM, limiting its use in canine immunology. This study quantizes SpA reactivity with canine immunoglobulins, revealing significant unreactive portions.
Area of Science:
- Immunology
- Biochemistry
- Veterinary Medicine
Background:
- Staphylococcal protein A (SpA) is widely used in immunoassays and immunoglobulin purification due to its high affinity for immunoglobulins.
- However, SpA exhibits variable reactivity with different immunoglobulin subclasses and species, including inconsistent reports for canine immunoglobulins.
- Previous observations suggested lower SpA reactivity with canine immunoglobulins than recent studies indicated.
Purpose of the Study:
- To quantitatively reevaluate the binding affinity of canine IgG and IgM to Cowan I strain SpA.
- To determine the extent of SpA reactivity with canine immunoglobulins under specific laboratory conditions.
- To assess the implications of SpA's binding characteristics for its utility in canine immunological procedures.
Main Methods:
- Purification of canine IgG and IgM from pooled plasma using affinity chromatography with specific polyclonal antibodies.
- Assessment of SpA reactivity via affinity chromatography using a SpA-agarose column, analyzing flow-through and eluate fractions.
- Quantification of SpA-bindable and non-bindable immunoglobulin fractions using absorbance at 280 nm and a solid-phase immunoradiometric assay (IRMA) with 125I-SpA.
Main Results:
- Approximately 18% of affinity-purified canine IgG and 33% of affinity-purified canine IgM did not bind to the SpA affinity column.
- Both non-bindable IgG and IgM fractions were unreactive with 125I-SpA in the IRMA.
- A secondary analysis using a different anti-canine IgG antibody confirmed that about 21% of purified canine IgG was unreactive with SpA.
Conclusions:
- SpA demonstrates incomplete reactivity with both canine IgG and IgM.
- A significant proportion of canine immunoglobulins do not bind to SpA, challenging its broad applicability in canine immunology.
- The findings necessitate careful consideration of SpA's limitations when used for canine immunoglobulin purification or in immunoassays.