Antibodies elicited by a serotype A

Antibodies elicited by a serotype A. either the rate of C3 accumulation or the amount of bound C3. When the classical pathway was blocked, group II and III MAbs markedly suppressed C3 binding that normally would have occurred via the alternative pathway. In contrast, MAbs of group IV had no effect on alternative pathway-mediated C3 binding. These results indicate that anticapsular antibodies with different epitope specificities may have distinct regulatory effects on activation and binding of C3. is the etiological agent of cryptococcal meningitis, a life-threatening contamination of particular importance in Slc2a3 patients with deficiencies in cellular immunity, most notably patients with the AIDS. The yeast is usually surrounded by a polysaccharide capsule that is composed primarily of glucuronoxylomannan (GXM), which has a linear (13)–d-mannopyranan backbone bearing -d-xylopyranosyl, -d-glucopyranosyluronic acid, and O-acetyl substituents (3, 9, 54). The cryptococcal capsule occurs as four major serotypes (A, B, C, and D) and is an essential virulence factor for the yeast. One of the most striking features of the cryptococcal capsule is usually its ability to activate the alternative complement pathway. Incubation of encapsulated cryptococci in normal human serum (NHS) leads to the deposition of 107 to BYL719 (Alpelisib) 108 C3 fragments around the yeast (28, 56). The C3 is usually deposited at the surface and throughout the capsule (30). Available evidence indicates that the amount of anti-GXM antibodies found in NHS is not sufficient to initiate the classical pathway (24); consequently, activation and binding of C3 to the cryptococcal capsule are mediated entirely by the alternative complement pathway (29, BYL719 (Alpelisib) 30, 55). One of the hallmark features of alternative pathway deposition of C3 onto encapsulated cryptococci is usually a delay of 5 to 8 min before readily detectable amounts of C3 are found on yeast cells incubated in NHS (29, 55). Once past the initial lag, C3 fragments rapidly accumulate around the yeast cells as incubation proceeds for an additional 10 min. Recently, there has been interest in antibody-mediated BYL719 (Alpelisib) resistance to cryptococcosis. Monoclonal antibodies (MAbs) have been proposed for treatment of cryptococcosis (7), and immunization with GXM-protein conjugates has been suggested for prevention of cryptococcosis (6, 12, 13). However, it is usually becoming increasingly clear that anti-GXM MAbs may have distinct specificities and biological activities. Anti-GXM MAbs which differ in (i) reactivities with GXM of the four major serotypes (2), (ii) apparent binding sites in the cryptococcal capsule (32, 37), and (iii) abilities to provide protection in a murine model of cryptococcosis (32, 37) have been described. Some differences in biological activity are related to differences in the epitope specificities of the various MAbs (32, 37). One means by which antibodies could enhance resistance to cryptococcosis is usually through accelerated deposition of opsonic C3 fragments via the action of the classical pathway. Such an acceleration would reduce or eliminate the 5- to 8-min lag that occurs during option pathway-mediated deposition of C3 fragments. The objectives of our study were to evaluate the effects of anti-GXM MAbs around the kinetics and BYL719 (Alpelisib) sites for deposition of C3 fragments into the cryptococcal capsule. We examined several well-characterized antibodies that differed in the epitope specificity of the MAbs. The results showed that MAbs with different isotypes and epitope specificities had distinctly different effects on activation and binding of C3 via the classical and alternative pathways; many antibodies markedly suppressed C3 binding, some antibodies accelerated C3 binding, and other antibodies had little or no effect. MATERIALS AND METHODS Yeast cells. 388 is an encapsulated isolate of serotype A that was used throughout the study. The yeast cells BYL719 (Alpelisib) were produced at 30C on a synthetic medium (8), killed by treatment overnight with 1.0% formaldehyde, washed with sterile 0.01 M phosphate-buffered 127.