Recombinant therapeutic antibody solutions at high protein concentrations often appear to be opalescent visually. Although this phenomenon is well-known, its mechanism remains to be elucidated. Opalescence behaviors for an IgG2 in salt solutions have been examined at different conditions including pH, salt concentration, temperature, and protein concentration. The experimental results suggest that the opalescence behaviors are dominated by critical opalescence, the enhanced density fluctuation occurring near the vicinity of the critical point on the liquid�liquid coexistence curve in the temperature�protein concentration phase diagram.  The enhanced density fluctuation has been confirmed by the observation of the droplet formation using microscopy.  Away from the critical point, the opalescence behavior is more closely related to the antibody self-association (agglomeration) caused by the attractive interactions between protein molecules. Furthermore, there is a surprising nonmonotonic relationship between opalescence and salt concentration when the solution pH is away from the pI.

Opalescence behaviors of a monoclonal antibody at high protein concentrations as related to liquid-liquid phase separation

243rd National Meeting (2012)

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