Dynamic changes in the morphology of Cryptococcus neoformans during murine pulmonary infection

Abstract

The pathogenesis of Cryptococcus neoformans infection has been studied extensively with respect to inflammatory and pathological changes, but very little information is available regarding the morphology of yeast cells during the course of infection. Electron microscopy of Cryptococcus neoformans in murine pulmonary infection revealed increased cell wall thickness with time, but this difference was only partially accounted for by increases in cell diameter. Cell walls of melanized cells were thicker than those of nonmelanized cells 2 h after infection, and the cell wall of yeast became blacker with time, suggesting that melanization contributes to the increased cell wall thickness. Heterogeneous cell populations emerged, with the appearance of giant forms. While for C. neoformans ATCC strain 24067 (serotype D) the full spectrum of cell sizes were observed, for strains H99 (serotype A) and 3501 (serotype D) cells were divisible into two populations, giant and micro forms. In contrast to cellular heterogeneity, the epitope recognized by a protective mAb on the capsular glucuronoxylomannan (GXM) was found at all times of infection. Immunoelectron microscopy using mAbs to GXM demonstrated reactivity with intracellular structures, suggesting that synthesis of capsular polysaccharide occurs, at least in part, in the cytoplasm. In summary, the results indicate that : (i) the infection is dynamic with respect to yeast cell morphology ; (ii) giant cell forms arise in tissue during the course of infection ; (iii) cell walls blacken and thicken during the course of infection, consistent with melanin synthesis during infection ; and (iv) GXM epitopes are found in the capsule, cell wall and cytoplasm, consistent with intracellular polysaccharide synthesis. The results indicate that the population of C. neoformans cells in tissue is in a highly dynamic state, implying that the immune system must confront cells with varying characteristics during the course of infection.

Capsule Structure Changes Associated with Cryptococcus neoformans Crossing of the Blood-Brain Barrier

“…Furthermore, it is possible however that prolonging the observation period would have uncovered additional alterations in the capsule structure. 36 Microevolutions and phenotypic switching have been reported for C. neoformans both in vitro and in vivo. 10,[37][38][39][40] A progressive increase in cell wall thickness as a function of time of infection (2 hours to 28 days) and an heterogeneity in capsule size have been reported during murine pulmonary infection.…”

Características histomorfológicas e histoquímicas determinantes no diagnóstico da criptococose em animais de companhia

“…Estudos realizados em casos de criptococose humana e infecções experimentais em animais têm também demonstrado variações na espessura da cápsula, na parede e no diâmetro da célula das leveduras de acordo com o órgão analisado e o tempo de infecção (Feldmesser et al 2001, Del Poeta 2004, Charlier et al 2005, Xie et al 2012. Diversos autores têm sugerido que o espessamento da cápsula ocorre principalmente em leveduras maduras devido à adição de novos polissacarídeos e nanoproteínas à estrutura pré-existente (Charlier et al 2005, McFadden et al 2006.…”

“…Essa diferença na localização entre leveduras pequenas e grandes pode estar relacionada principalmente com relação a abundância de cápsula, tamanho da célula ou localização da levedura em determinados órgãos. Estudos têm demonstrado que leveduras menores e com pouca cápsula foram observadas principalmente no interior de macrófagos devido à facilidade de opsonização e formação de fagolisossomas no interior de macrófagos (Xie et al 2012), enquanto que leveduras grandes, com cápsula abundante, eram observadas principalmente livres nos tecidos (Feldmesser et al 2001, Okagaki et al 2010.…”

“…A variação no tamanho da célula das leveduras é um achado constante nas infecções em humanos e em animais (Feldmesser et al 2001, Okagaki et al 2010, Xie et al 2012. No entanto, neste estudo não foram observadas leveduras com células de tamanho gigante (denominadas "células titãs"), como descritas em alguns casos de criptococose com envolvimento pulmonar (em humanos e camundongos), as quais podem atingir até 100µm de diâmetro (Feldmesser et al 2001, Okagaki et al 2010.…”

“…No entanto, neste estudo não foram observadas leveduras com células de tamanho gigante (denominadas "células titãs"), como descritas em alguns casos de criptococose com envolvimento pulmonar (em humanos e camundongos), as quais podem atingir até 100µm de diâmetro (Feldmesser et al 2001, Okagaki et al 2010.…”