Circular dichroism of immune complexes with rheumatoid factor activity.

The circular dichroism (CD) of IgG complexes with RF activity and that of monomeric IgG without this activity, and isolated from the same individual, were compared. The IgG complexes had a significantly deviant CD spectrum in the near u.v. region, both before and after dissociation, whereas the monomeric IgG had a normal spectrum. Immunoglobulins were isolated from the same serum with the use of specific antiserum against unique determinants in some IgG complexes with RF activity. Both before and after dissociation the CD spectrum in the far u.v. region of these immunoglobulins differed significantly from that of the above-mentioned preparations. The results confirmed that the structure of IgG in the RF-active complexes differed from that of normal IgG. The immunoglobulins with the unique determinants had, in turn, a structure that was not found in the pool of the RF-active IgG molecules or in normal IgG.