Tissue invasiveness and non-acidic pH in human candidiasis correlate with "in vivo" expression by Candida albicans of the carbohydrate epitope recognised by new monoclonal antibody 1H4

Abstract

Background: The morphogenetic conversion between yeast and hyphal growth forms appears to be crucial in the pathogenesis of invasive candidiasis, and can be regulated by environmental signals such as extracellular pH.

Aims: To characterise the epitope recognised by monoclonal antibody 1H4, and to evaluate the expression of its corresponding epitope in Candida albicans cells under different conditions of pH and temperature, and "in vivo", in tissue samples from patients with human candidiasis.

Methods: Monoclonal antibody 1H4 was generated against the 58 kDa cell wall mannoprotein of C albicans (mp58), and was further characterised by immunoblot analysis, periodate treatment of the antigenic preparations, and agglutination experiments of C albicans strains 3153A, SC5314, and 412, cultured under different environmental conditions (growth media and pH). An immunohistochemical study was performed in 24 human tissue samples from patients with mucocutaneous and systemic candidiasis.

Results: 1H4 recognises a pH sensitive carbohydrate epitope on the surface of C albicans cells, and this epitope is not restricted to mp58, but is shared with other cell wall mannoproteins. Immunohistochemical findings indicated that expression of the 1H4 epitope on C albicans cells in tissue sections from human candidiasis correlates with tissue invasion and pH of the niche. 1H4 immunoreactivity was also found in candida remnants within macrophages.

Conclusions: The fact that 1H4 epitope expression selectively identifies invasive forms of C albicans, in addition to candida remnants within macrophages, supports its potential value in the diagnosis and management of human candidiasis.

Figure 1

Immunoblot analysis to assess the reactivity of monoclonal antibody 1H4 with Candida albicans cell wall materials. (A) Reactivity of a rabbit polyclonal antiserum containing antibodies against most moieties present in the C albicans β mercaptoethanol extract. (B) Reactivity of monoclonal antibody 1H4 against materials present in the cell wall extracts.

Figure 2

Effect of periodate oxidation of Candida albicans mp58 and a C albicans β mercaptoethanol (βME) extract on monoclonal antibody 1H4 reactivity examined by a modified enzyme linked immunosorbent assay. Values are expressed as per cent reactivity compared with control (untreated) samples (100%). Error bars indicate standard deviations. Black bars, untreated samples; shaded bars, 10mM sodium periodate treatment.

Figure 3

1H4 immunoreactivity in human candidiasis. (A) Invasive candidiasis of the oesophagus, showing positive mycelial cells. (B, C) Systemic candidiasis; positive yeast cells in the liver (B); both mycelial and yeast cells showing immunoreactivity in the thyroid (C). (D–F) Invasive gastric candidiasis; 1H4 negative yeasts are the predominant form in the superficial part (D and E); numerous 1H4 positive invading mycelial cells are seen in the deep part (F). (G) Systemic candidiasis; 1H4 immunostaining is detected in fungal remnants within the cytoplasm of tissue macrophages (immunoperoxidase, haematoxylin counterstain).