Spontaneous activation of reconstituted and serum C1 and the role of C1-inhibitor.

Evidence will be presented that first order, spontaneous activation of solution C1 at 37 degrees C under physiological conditions is a very slow process with a half-life of the order of one day and perhaps considerably longer. In addition, negative evidence will be presented showing that the formation of functionally significant levels of a complex between C1-Inhibitor and unactivated C1 does not occur. Such a complex had been previously postulated to explain the strong inhibition of the spontaneous activation of C1 which was observed upon the addition of C1-Inhibitor.

A mechanism for the spontaneous activation of the first component of complement, C1, and its regulation by C1-inhibitor.

We have developed a method to initiate spontaneous activation of the first component of complement in serum, by the removal of C1-inhibitor through complexation with added C1s. Preliminary experiments to test this method using C1 reconstituted from its purified subcomponents led to an unexpected result: pre-incubation of the reassembled subcomponents with C1-inhibitor, followed by its removal with C1s, altered the subsequent pattern of spontaneous activation. Thus, pre-incubation with C1-inhibitor at 37 degrees C for 1 h resulted in sigmoidal activation of C1 with a prolonged lag phase.

Kinetics of C1 activation by a monoclonal anti-C1q antibody and its (Fab)2 fragments.

Monoclonal antibody 1H11, which binds to the "head" portion of C1q, has been shown to be a strong, stoichiometric activator of C1, the first component of human complement, maximal activation being achieved at a ratio of one antibody-combining site per one C1q head; moreover, this activation occurs even in the presence of C1-inhibitor, as reported previously. In the present paper, the kinetics of activation are shown to be biphasic; that is, a portion of the C1 is activated very rapidly, and the remainder slowly. These two processes can be separated by the order of mixing of preincubated components; thus, only the rapid activation rate is observed if C1q and the monoclonal antibody are preincubated together and are added subsequently to a mixture of C1r2C1S2 and C1-inhibitor.

Ecto-5'-nucleotidase activity in lymphoblastoid cell lines derived from heterozygotes for congenital X-linked agammaglobulinemia.

Lymphoblastoid cell lines were established from female relatives of patients with congenital X-linked-agammaglobulinemia by Epstein-Barr virus transformation of their peripheral B lymphocytes. Cell lines derived from presumed carriers were characterized by low ecto-5'-nucleotidase activity and a reduced percentage of surface immunoglobulin-bearing cells. Measurement of ecto-5'-nucleotidase activity in newly established lymphoblastoid cell lines may provide a means for the identification of heterozygotes for congenital X-linked agammaglobulinemia.