Inverse association between IgG–anti-κ autoantibody and CA in cold agglutination caused by noninfectious agents. In patients (A) without (n = 165) and (B) with (n = 120) recent infections, the anti-κ and CA autoantibody were determined (left and right ordinate). Sera with identical CA titers were included in the same group (abscissa). Anti-κ titers are given in OD 405 nm (median ± MAD).