A new fixative allowing accurate immunostaining of kappa and lambda immunoglobulin light chain expressing B-cells without antigen retrieval in paraffin-embedded tissue

To detect immunoglobulin expression in formaldehyde-fixed, paraffin-embedded tissue, an enzyme and/or microwave-retrieval treatment is necessary for antigen epitope recognition, which has the well-known disadvantages of impaired tissue morphology and often high background staining. Here, we report a new fixative mixture of methanol, formaldehyde, glacial acetic acid, and polyethylene glycol (MFA) that makes it possible to detect kappa and lambda immunoglobulin light chain expression in various paraffin-embedded tissues of human and rat origin without the application of any antigen-retrieval method. Both tissue morphology and immunoreactivity of MFA-fixed tissue samples are excellent. With double immunostaining (method 1), both kappa or lambda immunoglobulin light chain-expressing plasma cells clearly can be demonstrated in the same section. The presence of kappa or lambda light chains in the smaller B-cells can also be detected by using more concentrated primary antibodies or by prolonging the incubation time (method 2). The flexibility of both the fixation and rinsing duration make the method convenient to use. The marked improvement of immunoreactions with MFA fixed, paraffin-embedded lymphoid tissue could have a notable impact on immunohistochemistry in diagnosis and research.