Delayed-type hypersensitivity responses in infected mice elicited by cytoplasmic fractions of Cryptococcus neoformans

Abstract

Four subcellular fractions of Cryptococcus neoformans prepared by differential centrifugation of disrupted whole yeast and a 3-day culture filtrate were examined for their ability to elicit delayed-type hypersensitivity in sensitized animals. The methods used to detect sensitization were (i) the footpad swelling test and inhibition of peritoneal macrophage migration in mice and (ii) skin testing in guinea pigs. Two entities, the post-mitochondrial supernatant and the culture filtrate, showed considerable activity in the footpad test, with 26-and 30-,A 24-h swellings, respectively, at 6 weeks after infection. With the latter there was interference from a strong antibody-mediated 4-h skin reaction. The post-mitochondrial supernatant produced strong delayed-type hypersensitivity in guinea pigs at a dose of 69 ,ug, and there was no demonstrable cross-reactivity in animals sensitized with heterologous fungi. The footpad swelling in mice correlated well with the macrophage migration inhibition test, with 71% inhibition in mice infected subcutaneously with C. neoformans at 6 weeks. However, mice infected intravenously developed poorer cell-mediated immunity than the subcutaneously infected mice. The post-mitochondrial supernatant was found to contain detectable amounts of cryptococcal capsular polysaccharide.

Encapsulation of Cryptococcus neoformans impairs antigen-specific T-cell responses

“…Experimental evidence also supports a primary role for T cell-dependent resistance, since athymic nude mice show increased susceptibility to infection (4,14) and resistance in normal animals is dependent on the presence of CD4+ T cells in vivo (17,27). However, previous studies of T-cell immunity to C. neoformans have focused on delayed-type hypersensitivity responses in vivo (10,13,16,25) or the development of T cell-mediated suppressor cell networks (28). In the present study we have extended these observations by investigating the characteristics of T-cell activation by C. neoformans in vitro.…”

The skin and systemic fungal infections

“…The importance of cellular immunity in limiting fungal invasion has been emphasized in the past (Krick & Remington, 1976) and it can be shown in experimental infections, e.g. cryptococcosis (Hay & Reiss, 1978) that introduction of the organisms into subcutaneous tissue as opposed to the blood stream produces excellent cellular immune responses. If this also occurs in humans it may explain the rarity of dissemination when fungal organisms enter via this route.…”

Cryptococcal skin test antigen: preparation variables and characterization

“…There is no lack of candidate cryptococcal antigens with which to pursue such studies, although none has been compared with another. Successful demonstrations of delayed hypersensitivity reactions have been reported in mice (7,8,13), guinea pigs (1,3,13,16), human volunteers (3,4,6,12,15), and cryptococcosis patients (1,3,6,17). In the last category were groups of 25 (3), 27 (17), and 38 (1) patients from this institution and 8 patients from another (6).…”