Opsonization of Cryptococcus neoformans by a family of isotype-switch variant antibodies specific for the capsular polysaccharide

Abstract

A family of immunoglobulin isotype-switch variants was isolated by sib selection from a murine hybridoma which produced an immunoglobulin G subclass 1 (IgGl) antibody specific for the capsular polysaccharide of Cryptococcus neoformans. Antibodies of the IgGl, IgG2a, and IgG2b isotypes had similar serotype specificity patterns in double immunodiffusion assays which used polysaccharides of the four cryptococcal serotypes as antigens. A quantitative difference in the ability of the isotypes to form a precipitate with the polysaccharide was observed in a double immunodiffusion assay and confirmed in a quantitative precipitin assay. The relative precipitating activity of the antibodies was IgG2a > IgGl >> IgG2b. Analysis by enzyme-linked immunosorbent assay of the reactivity of the three isotypes with cryptococcal polysaccharide showed identical titers and slopes, suggesting that the variable region of the class-switch antibodies was unaltered. This system allowed us to examine the effect of the Fc portion of the antibody on opsonization of encapsulated cryptococci. Yeast cells were precoated with antibodies of each isotype and incubated with murine macrophages or cultured human monocytes. Antibodies of all three isotypes exhibited a dose-dependent opsonization for phagocytosis by both human and murine phagocytes. The relative opsonic activity of the antibodies was IgG2a > IgGl > IgG2b.

Antibody isotype-specific engagement of Fcγ receptors regulates B lymphocyte depletion during CD20 immunotherapy

“…These results also further support previous fi ndings whereby Ab isotypes exhibit functional hierarchies in their relative abilities to engage diff erent FcγRs in vivo. The current immunotherapy studies also correlate with models of adaptive immunity where IgG2a Abs are most effi cient in providing optimal or substantial protection during bacterial, viral, and fungal infections (41)(42)(43)(44)(45). Thus, the intricate innate eff ector pathways used for B cell depletion in the current studies may have been selected evolutionarily for potency.…”

Protective and nonprotective monoclonal antibodies to Cryptococcus neoformans originating from one B cell.

“…,eoformans (11)(12)(13)(14)(15). In contrast to GXM, the GXM-TT vaccine is highly immunogenic (10) and elicits antibody responses characteristic of T cell-dependent antigens with a predominance of IgG isotypes (10,16,17).…”

Variation in the structure of glucuronoxylomannan in isolates from patients with recurrent cryptococcal meningitis

“…The capsular exopolysaccharides may also contribute to virulence by causing suppression of the immune response (25,32,43,44), inhibiting leukocyte migration (17), and enhancing human immunodeficiency virus infection (35). In the absence of opsonins, phagocytosis of C. neoformans by host effector cells is inefficient (24,37). Antibodies to the capsular polysaccharide are potent opsonins (37) that form the bases of two strategies being developed for the prevention and treatment of cryptococcal infections: vaccination with GXM-protein conjugates (15) and passive antibody therapy (16,31).…”