Molecular and idiotypic analysis of antibodies to Cryptococcus neoformans glucuronoxylomannan

Abstract

Antibodies to the Cryptococcus neoformans capsular glucuronoxylomannan (GXM) form the basis of two potential therapeutic intervention strategies, i.e., conjugate vaccines and passive antibody therapy. To better understand the molecular basis of the antibody response, the heavy-and light-chain immunoglobulin variable region (V. and VL, respectively) sequences of seven monoclonal antibodies (MAbs) to GXM were determined. Rabbit anti-idiotypic serum was made to the previously characterized murine MAb 2H1 and used to study MAb 2H1 idiotype expression in other GXM-binding MAbs and immune sera. MAb El originated from a C3H/HeJ mouse immunized with C. neoformans serotype A polysaccharide. MAbs 471, 1255, 339, 3C2, 386, and 302 originated from BALB/c mice immunized with polysaccharide of serotypes A, A, B, C, D, and D, respectively, conjugated to sheep erythrocytes. In the El, VH uses V,1 from the T15 gene family and JH3 and has a D segment of three amino acids, and the VL uses a V,Ser-like gene family element and JK5. In MAbs 471 and 3C2, the VH uses VH7183-like gene family elements and JH2 and has D segments of seven amino acids, and the VL uses V,5.1 and J,1. In MAbs 1255 and 339, the V. uses VH10-like gene elements and JH4 and has six codon D segments, and the VL uses a V.21-like gene element and J.5. In MAbs 302 and 386, respectively, the VH uses V,GAM-like gene elements and JH2 and JH3 and has six and four codon D segments, and VL uses V,4/5-like gene elements and J,1. VH usage, MAb 2H1 idiotype expression, and fine specificity mapping define a minimum of three GXM epitopes which elicit protective antibodies. The results confinn that the antibody response is highly restricted, suggest a close relationship between molecular structure and serological properties, and provide insight into protein structural motifs important for GXM binding. Cryptococcus neofornans is an encapsulated fungus that causes life-threatening meningoencephalitis in up to 9% of patients with AIDS (53). Treatment of cryptococcal meningitis in patients with AIDS is difficult because antifungal drugs often

Molecular analysis of monoclonal antibodies to group variant capsular polysaccharide of : recurrent heavy chains and alternative light chain partners

“…3). Recurrent usage of light chain Vdomains in mice is consistent with V-gene usage to capsular PS in humans and in antibody responses to many other antigens (Casadeval et al, 1994;Fish and Manser, 1987;Griffiths et al, 1984;Patera et al, 1995;Scott et al, 1989). The relative absence of somatic mutations in the light chains V-genes suggests that the antibody responses were T-independent in nature.…”

“…A pattern of recurrence exists if the same or highly related antibody gene structures are produced to the same epitope in multiple individuals/animals (Kalinke et al, 1996;Kavaler et al, 1990;Mo et al, 1993;Solin et al, 1992). A B-cell response is termed a restricted response, which is an extreme case of recurrence, when the identical VK chain (Adderson et al, 1992;Akolkar et al, 1987;Casadeval et al, 1994;Mo et al, 1993;Patera et al, 1995;Scott et al, 1989), V H chain (Pascual et al, 1992), or both Ikematsu et al, 1998;Kaartinen et al, 1984;Liu et al, 1971) are predominantly found to encode antibodies to the same epitope of independently derived clones. All of these responses have in common an antigen with a repetitive structural organization, and/or induce a co-comittant T-cell-independent B-cell response, as they do not require mature T cells to elicit an antibody response.…”

Antibodies to theCryptococcus neoformanscapsular glucuronoxylomannan are ubiquitous in serum from HIV+ and HIV− individuals

“…Anticarbohydrate antibodies that persist for years [51,52] may be important mediators of protection. In murine cryptococcosis, protective anti-GXM MoAbs express specific heavy chain isotypes, may express a specific heavy chain idiotype, and recognize distinct GXM epitopes, whereas MoAbs that recognize the same epitope and express a different isotype are nonprotective [15,17]. Human serum, like murine serum, probably contains both protective and non-protective antibodies, and the latter could obscure the efficacy of a small subset of protective antibodies.…”

“…Murine anti-GXM antibodies elicited by infection and by GXM-tetanus toxoid (GXM-TT), a conjugate vaccine, enhance survival and reduce colony counts in C. /zeo/orOTan.$-infected mice [9,16]. Antibody idiotype and isotype specificity are important 425 determinants of protection in these models [17,18]. In the pre-AIDS era, anti-CPS antibodies were shown to be a good prognostic indicator in patients with CM [19].…”

“…Anti-CPS antibody-mediated protection in vivo, in vitro phagocytosis, and an improved prognosis in CM in the pre-AIDS era, all support a role for anti-CPS antibody in moderating or preventing cryptococcosis [9][10][11][12][13][14][15][16][17][18][19]. This study was undertaken to determine the prevalence of anti-GXM antibodies in HIV"^ and HIV~ individuals, and to determine if the development of CM in individuals with HIV infection can be correlated with antibody titre, isotype, or IgG subclass.…”