Lactate dehydrogenase (LDH)-IgG3 immunoglobulin complexes in human serum

Sera of fifteen patients containing complexes of LDH and IgG were analysed. The LDH-IgG complexes of fourteen of these patients were investigated for their subclass specificity. They appeared to consist of LDH and IgG3, except for one of the patients. The serum of the latter patient also contained complexes of LDH and IgG1. In this serum both types of the immunoglobulin light chains were involved in the formation of the complexes, whereas in the serum of the patients with LDH-IgG3 complexes alone, they only contained one of the two immunoglobulin light chain types; it mainly concerned kappa type. The results of the present study were compared to those of a previous study on LDH-IgA complexes, in which the IgA fraction always contained light chains of kappa type. The mean LDH activity and the heat stability of the LDH activity in the sera with LDH-IgA complexes appeared to be higher than in the sera with LDH-IgG3 complexes. In contrast to complexes of LDH and IgA which occurred in all age groups LDH-IgG3 complexes were mainly found in elderly persons. Although auto-antibodies to different tissue antigens were present in the majority of the sera containing LDH IgG3 complexes, antibodies to LDH could not be demonstrated. A relationship between the presence of the complexes in the serum and a particular disease could not be established.