Ecto 5'-nucleotidase deficiency in primary hypogammaglobulinaemia

The activity of the lymphocyte ectoenzyme 5'-nucleotidase is very low in the majority of patients with primary 'common variable' hypogammaglobulinaemia. In order to test whether this can be explained by lymphocyte subpopulation deficiencies we measured 5'-nucleotidase activity, using both biochemical and histochemical techniques, in purified T and B cells from patients and healthy subjects. Purified B cells from normal subjects have about four times the activity of T cells. This explains why the levels of lymphocyte 5'-nucleotidase activity are at the lower limit of the normal range in patients with X-linked hypogammaglobulinaemia who lack B cells. The low levels in the 'common variable' group can be explained by low activity in their T lymphocytes associated with either low activity in their B cells or depletion of B cells. The finding that inhibition of the enzyme does not interfere with in vitro lymphocyte transformation or immunoglobulin production in normal subjects indicates that the enzyme deficiency is not directly responsible for the hypogammaglobulinaemia. These and other studies suggest that this enzyme appears on lymphocytes at a certain stage of development and that both T and B lymphocytes in some patients with 'common variable' hypogammaglobulinaemia are developmentally immature.