Cell surface immunoglobulin. XIX. Susceptibility of IgD and IgM on murine splenocytes to cleavage by papain

The present studies were designed to determine the effect of papain upon IgM and IgD on the surface of murine splenocytes. By using radioiodinated cells, it was shown that IgD is more susceptible to cleavage by papain than IgM. The difference in susceptibility to papain of the two isotypes was not observed when cell lysates were employed, suggesting that attachment to the plasma membrane affects the accessibility of IgM to papain. The major site of attack of the enzyme on IgD appears to be in the hinge region. The possible biologic implications of such a cleavage are discussed.