The reaction between endotoxic lipopolysaccharide (LPS) and the guinea pig complement system was shown to proceed by way of an intermediate complex, LPS-X, which contains at least six guinea pig serum proteins. LPS-X, like EAC4,2a (sheep erythrocytes carrying antibody molecules and C4,2a complexes), destroys the C3 molecule by cleavage. On incubation at 370C, LPS-X loses its capacity to destroy C3 at about the same rate as the decay of EAC4,2a, so that it has been assumed that LPS-X carries C4,2a sites that are responsible for the destruction of C3.We have now shown that monospecific rabbit antiguinea pig C2, which effectively inhibits C3 cleavage by EAC4,2a, does not interfere with the destruction of C3 by LPS-X. Furthermore, not more than a trace of C2ad is released from LPS-X on incubation at 370C. These results indicate that LPS-X does not carry a significant quantity of C4,2a and, hence, that its capacity to destroy C3 is due to another factor which is presumably a component of the properdin system.On incubation of endotoxic lipopolysaccharide (LPS) from Gram-negative bacteria with guinea pig serum there occurs a complement fixation process which is unusual in that the late-acting complement (C) components C3, C5, C6, C7, C8, and C9 are destroyed, while the early-acting components Cl, C4, and C2 are not affected significantly (1). For this Abbreviations: C, C1, C2, C3, etc.: C refers to complement, and the numbers indicate the components of the C system._The letter "a,"Y as in C2a, refers to a fragment. The "bar" in C1, or C4,2a, indicates an enzymically active component or complex. Nomenclature of Bull. Wld. Hlh. Org., 39, 935 (1968 reason it has been proposed that the reaction between LPS and the C system follows an alternate pathway in which the early-acting C components are bypassed. Similar observations were made about two decades ago by Pillemer and associates (2) in studies of the reaction between zymosan, an insoluble carbohydrate from the cell wall of yeast, and the C system. These investigators also considered a kind of alternate pathway involving a previously unrecognized serum protein, which they named properdin.Studies (3) have shown that LPS does not react directly with C3 or with the other late-acting C components but proceeds by way of an intermediate, LPS-X, which is formed on brief incubation of LPS with guinea pig serum at 370C, and which comprises at least six guinea pig serum proteins, including gamma globulin and C3. LPS-X, unlike LPS, reacts directly with C3, destroying it by cleavage. LPS-X resembles the intermediate EAC4,2a (sheep erythrocytes carrying antibody molecules and C4,2a complexes), which cleaves C3 directly. Moreover, on incubation at 370C LPS-X loses its ability to destroy C3 at about the same rate as the decay of EAC4,2a. For these reasons, it has been proposed that LPS-X may carry C4,2a sites and that these are responsible for its ability to destroy C3. However, some have thought that this interpretation is at odds with the fact that the early-acting C componen...

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Antibody distinct from that involved in neutralization and directed to an antigen (AG-4) induced in HEp-2 cells by infection with herpesvirus type 2 was identified in serums from patients with cervical carcinoma by means of a quantitative micro complement fixation test. The presence of antibody to AG-4 correlates well with the extent of the tumor; antibody is virtually absent in matched control women and in women with therapy and without recurrent neoplasia. Reactivity is not observed with control antigen consisting of a cell extract prepared from uninfected HEp-2 cells. The possible prognostic significance of this antibody and its implications are discussed.