Effect of Petting a Dog on Immune System Function Descriptors: Random assignment to experimental and control groups

A number of influences on immune system function have been documented during the past several decades (see Cohen & Herbert, 1996, for a review). The effects of stress and negative psychological states have been

5 extensively studied (e.g., McLelland, Ross, & Patel, 1985). Far fewer studies have documented immunoenhancing effects. We have published several studies in which increases in Immunoglobulin A (IgA) were noted (see Chametski & Brennan, 2001, for a review).