Carbohydrate-rich high-molecular-mass antigens are strongly recognized during experimental Histoplasma capsulatum infection / Antígenos de alta massa molecular ricos em carboidratos são fortemente reconhecidos durante infecção experimental por Histoplasma capsulatum

INTRODUCTION: During histoplasmosis, Histoplasma capsulatum soluble antigens (CFAg) can be naturally released by yeast cells. Because CFAg can be specifically targeted during infection, in the present study we investigated CFAg release in experimental murine histoplasmosis, and evaluated the host humoral immune response against high-molecular-mass antigens (hMMAg. >150 kDa), the more immunogenic CFAg fraction. METHODS: Mice were infected with 2.2x10(4) H. capsulatum IMT/HC128 yeast cells. The soluble CFAg, IgG anti-CFAg, IgG anti-hMMAg, and IgG-hMMAg circulating immune complexes (CIC) levels were determined by enzymelinked immunosorbent assay, at days 0, 7, 14, and 28 post-infection. RESULTS: We observed a progressive increase in circulating levels of CFAg, IgG anti-CFAg, IgG anti-hMMAg, and IgG-hMMAg CIC after H. capsulatum infection. The hMMAg showed a high percentage of carbohydrates and at least two main immunogenic components. CONCLUSIONS: We verified for the first time that hMMAg from H. capsulatum IMT/HC128 strain induce humoral immune response and lead to CIC formation during experimental histoplasmosis.

INTRODUÇÃO: Durante a histoplasmose, os antígenos solúveis de Histoplasma capsulatum (CFAg) podem ser liberados naturalmente pelas células leveduriformes. Considerando que os CFAg constituem um alvo específico durante a infecção, no presente estudo nós investigamos a liberação de CFAg durante a histoplasmose murina experimental, e avaliamos a resposta imune humoral do hospedeiro contra antígenos de alta MM (hMMAg; >150 kDa), altamente imunogênicos. MÉTODOS: Camundongos foram infectados com 2.2x10(4) leveduras de H. capsulatum, cepa IMT/HC128. Os níveis de CFAg solúveis, IgG anti-CFAg, IgG anti-hMMAg, e também de imunocomplexos circulantes (CIC) IgG-hMMAgs foram determinados por ELISA nos dias 0, 7, 14 e 28 após a infecção. RESULTADOS: Após a infecção por H. capsulatum, observamos um aumento progessivo de CFAg circulantes, IgG anti-CFAg, IgG anti-hMMAg, e também de CIC IgG-hMMAgs. Os hMMAg apresentaram alta porcentagem de carboidratos e, pelo menos, dois componentes imunogênicos. CONCLUSÕES: Mostramos pela primeira vez que os hMMAg de H. capsulatum cepa IMT/HC128 induzem resposta imune humoral e levam à formação de CIC durante a histoplasmose experimental.

Participation of N-acetyl-D-glucosamine carbohydrate moieties in the recognition of Schistosoma mansoni sporocysts by haemocytes of Biomphalaria tenagophila

Lectin-carbohydrate binding may be involved in the recognition of Schistosoma mansoni sporocysts by haemocytes of Biomphalaria; therefore, we tested if this interaction is associated with snail resistance against Schistosoma infection. In vitro data showed that most of the S. mansoni sporocysts cultured with haemocytes from Biomphalaria glabrata BH, a highly susceptible snail strain, had a low number of cells that adhered to their tegument and a low mortality rate. Moreover, the addition of N-acetyl-D-glucosamine (GlcNAc) did not alter this pattern of adherence and mortality. Using haemocytes and haemolymph of Biomphalaria tenagophila Cabo Frio, we observed a high percentage of sporocysts with adherent cells, but complete encapsulation was not detected. Low concentrations of GlcNAc increased haemocyte binding to the sporocysts and mortality, which returned to basal levels with high concentrations of the carbohydrate. In contrast, haemocytes plus haemolymph from B. tenagophila Taim encapsulated cellular adhesion index of level 3 and destroyed over 30 percent of the S. mansoni sporocysts in culture. Interestingly, the addition of GlcNAc, but not mannose, to the culture medium resulted in the significant inhibition of cellular adhesion to the parasite tegument and the reduction of parasite mortality, suggesting that GlcNAc carbohydrate moieties are important to the recognition of S. mansoni by B. tenagophila Taim.

The interaction between Histoplasma capsulatum cell wall carbohydrates and host components: relevance in the immunomodulatory role of histoplasmosis

Histoplasma capsulatum is an intracellular fungal pathogen that causes respiratory and systemic disease by proliferating within phagocytic cells. The binding of H. capsulatum to phagocytes may be mediated by the pathogen's cell wall carbohydrates, glucans, which consist of glucose homo and hetero-polymers and whose glycosydic linkage types differ between the yeast and mycelial phases. The ±-1,3-glucan is considered relevant for H. capsulatum virulence, whereas the ²-1,3-glucan is antigenic and participates in the modulation of the host immune response. H. capsulatum cell wall components with lectin-like activity seem to interact with the host cell surface, while host membrane lectin-like receptors can recognize a particular fungal carbohydrate ligand. This review emphasizes the relevance of the main H. capsulatum and host carbohydrate-driven interactions that allow for binding and internalization of the fungal cell into phagocytes and its subsequent avoidance of intracellular elimination.

Immunochemical characterization of carbohydrate antigens from fungi, protozoa and mammals by monoclonal antibodies directed to glycan epitopes

Cell surface carbohydrates constitute the major antigenic determinants of fungi and protozoa. Glycoconjugates also represent a large variety of antigens or markers present in mammals such as histo-blood groups ABO, differentiation and heterophile antigens, among others. This article focuses on the general properties of glycoconjugate antigens and production and characterization of the anti-carbohydrate monoclonal antibodies (MoAbs). It describes the specificity and some properties of monoclonal antibodies directed against carbohydrate epitopes present in tumor-associated glycoproteins, in clycosaminoglycans of higher eukaryotes and in glycolipid antigens of protozoa and fungi. The epitopes recognized by the anti-carbohydrate MoAbs range from one sugar unit up to ten sugar units. Although most anti-carbohydrate MoAbs are directed predominantly toward terminal sugar residues, a few MoAbs are also reactive with internal sugar residues. The fine structure of the carbohydrate epitopes has been chemically defined by [H]NMR, GC/MS of alditol acetates of partially permethylated compounds, FAB/MS, degradation with exoglycosidases and inhibition with different methyl-glycosides and oligosaccharides.

Comparison of the circulating carbohydrate antigen and the anti-SWAP antibodies in patients with active schistosoma haematobium infection

Twenty five patients, with age ranged from 5-25 years [mean +/- SD: 12.8 +/- 4.7] with active S. haematobium infection were investigated in the present study. They were subjected to complete clinical history, examination, abdominal ultrasonography and urine and stool examination. Nuclepore filtration method for quantitation of S - haematobium ova was performed. Immunological assays to study the levels of circulating carbohydrate antigen lusing monoclonal antibody 128 C3/3/21] and anti-SWAP [soluble adult worm antigen preparation] immunoglobulins IgG1, IgG4 and IgE were performed. The patients were re-evaluated again at 1, 3 and 6 months of receiving praziquantel therapy. It was found that all Patients had significantly high circulating carbohydrate antigen in their sera i.e. above the cut-off value. Also, there was a significant drop in the mean circulating antigen levels at 1, 3 and 6 months after praziquantel treatment. However, the levels of the circulating antigen did not reach to the cut-off value in, 12 patients 6 months after treatment; 5 of these patients had evidence of reinfection and/or persistence of infection. On the other hand, all the patients had positive ELISA reaction for IgGl and IgG4, while 5 patients had negative reaction for IgE through the different visits before and after treatment. The decrease in the mean levels of IgGl and IgG4 was statistically significant only after 6 months of treatment; but the mean levels of IgE showed significant drop at 3 and 6 months after treatment. These findings suggested that the detection of circulating carbohydrate antigen is more accurate in diagnosis of active infection, reinfection-and in evaluating the efficacy of treatment. We found a significant correlation between the circulating carbohydrate antigen levels and the anti-SWAP IgE during the active infection but no significant correlation was found between the antigen levels and IgGl and IgG4. This may be attributed to the fact that IgE antibodies to S- haematobium adult worm antigen increase with the parasite load. Further evaluation must be performed on a large number of patients with more prolonged period of follow-up

Carbohydrate epitopes: structure and presentation and the reactivity of biological ligands: recognition of alpha-D-Galp NAc and alpha-D-Galp conformational structures

Apart from glycolipids and glycoproteins that express A and B blood group antigens which contain terminal nonreducing units of alpha-D-Galp NAc and alpha-D-Galp respectively, there are several other glycoconjugates in nature that contain these units linked to unfucosylated saccharides or protein. They represent normal products of the action of specific glycosyl-transferases in primate and nonprimate mammalian cells, protozoa and a few other microorganisms, end-units of carbohydrate components that have not benn further processed by additional glycosylation, or neo-antigens resulting from deregulation of certain transferases as in tumor cells. Biological ligands recognizing these structures include mono and polyclonal antibodies, bacterial fimbriae and laminin. Binding depends on the linkages and sequence of the carbohydrate chain, but also on the epitope conformation as influenced by adjacent substitution, angling determined by the glycoconjugate-substrate interaction, steric hindrance and other factors. These aspects are discussed in this minireview.