Host defense against Neisseria meningitidis requires a complement-dependent bactericidal activity.

Some individuals, with severe or recurrent infection with Neisseria species, have been identified as lacking a component in the terminal attack sequence of complement (complement components 5 to 9). The relevance of the terminal attack sequence to various phases of host defense was tested with the use of the C-11 strain of meningococci and human serum genetically deficient in complement component 8 (C8-D). The C8-D serum was comparable to normal serum in supporting ingestion and intracellular killing by leukocytes but was not bactericidal in the fluid phase unless reconstituted with C8.

Structural features and biologic properties of fragments obtained by limited proteolysis of C3.

Limited proteolysis of the third component of human complement (C3) was performed by using trypsin and streptococcal proteinase and the digests were analyzed for biologic activity. Incubation of C3 with trypsin for 1 min yielded a peptide with smooth muscle-contracting activity but no chemotactic activity, whereas the digest obtained after 15 min of incubation had only chemotactic activity. The conversion of muscle contracting to chemotactic activity could be correlated with the time course of trypsin hydrolysis.