Inclusion Bodies

A characteristic morphological change in cells infected by certain viruses is the formation of inclusion bodies (or inclusions) which are recognized by light microscopy following fixation and staining (Fig. 5-3). Depending on the virus, inclusion bodies may be single or multiple, large or small, intranuclear or intracytoplasmic, round or irregular in shape, and acidophilic (stained by eosin) or basophilic (stained by hematoxylin).

The most striking viral inclusion bodies are the intracytoplasmic inclusions found in cells infected with poxviruses, paramyxoviruses, reoviruses.

Fig. 5-1 Unstained confluent monolayers of the three main types of cultured cells, as they appeal by low-power light microscopy, through the wall of the glass or plastic vessel in which the refls are cultured Magnification >'60 (A) Primary monkey kidney epithelium a mixed population of mainly epithelial cclts taken freshly from the bodv (B) Diploid strain of human fetal fibroblasts ((.') Continuous (me of malignant epithelial tells (Courtesy I. Jack )

Fig. 5-1 Unstained confluent monolayers of the three main types of cultured cells, as they appeal by low-power light microscopy, through the wall of the glass or plastic vessel in which the refls are cultured Magnification >'60 (A) Primary monkey kidney epithelium a mixed population of mainly epithelial cclts taken freshly from the bodv (B) Diploid strain of human fetal fibroblasts ((.') Continuous (me of malignant epithelial tells (Courtesy I. Jack )

Flg. 5-2 Cytopathic effects produced by different viruses The cell monolayers are shown as they would normally be viewed in the laboratory, (infixed and unstained Magnification. *60 (A) Fnterovirus. rapid rounding of cells, progressing to complete cell lysis (B) Herpesvirus local areas of swollen rounded cells (C) Paramyxovirus total areas of cells are fused to form syncytia (D) [ lemad sorption erythrocytes adsoib to infected cells that incorporate hemagglutinin into the plasma membrane (Couilesv I Jack )

Fig. 5-3 types of vrral inclusion bodies (hematoxylin and eosm stain) Magnification- X200 (A) Intranuclear inclusions and syncytium (herpesvirus) Small arrow, nucleolus, large arrow, inclusion body Note marginatum of condensed nuclear chromatin separated from inclusion body by a halo (R) intracytopfasrmc inclusions (reovirus). Arrows indicate inclusion bodies, mainly in perinuclear locations (C) Intranuclear and intracyloplasmic inclusions and syncytia (measles virus). Small airow, intracyloplasmic inclusion body, large arrow, intranuclear inclusion body. (Courtesy I Jack )

Fig. 5-3 types of vrral inclusion bodies (hematoxylin and eosm stain) Magnification- X200 (A) Intranuclear inclusions and syncytium (herpesvirus) Small arrow, nucleolus, large arrow, inclusion body Note marginatum of condensed nuclear chromatin separated from inclusion body by a halo (R) intracytopfasrmc inclusions (reovirus). Arrows indicate inclusion bodies, mainly in perinuclear locations (C) Intranuclear and intracyloplasmic inclusions and syncytia (measles virus). Small airow, intracyloplasmic inclusion body, large arrow, intranuclear inclusion body. (Courtesy I Jack )

and rabies virus and the intranuclear inclusion bodies found in cells infected with herpesviruses, adenoviruses, and parvoviruses. Some viruses, for example, measles virus and cytomegalovirus, may produce both nuclear and cytoplasmic inclusion bodies in the same cell. Many inclusions have been shown to be accumulations ol viral structural components; for example, the intra-cytoplasnnc inclusions in cells infected with rabies virus or in "inclusion body encephalitis" (subacute sclerosing encephalopathy, caused by measles virus) are masses of viral nucleocapsids. The basophilic mtracytoplasmic inclusions invariably found in cells infected with poxviruses are sites of viral synthesis (viral "factories") made up of masses of viral protein and nucleic acid. In a few instances, for example, adenoviruses in the nucleus and reoviruses in the cytoplasm, inclusion bodies represent crystalline aggregates of virions. Other inclusion bodies, such as those found in the nucleus of cells infected with herpesviruses, are the result of late degenerative changes, as well as condensation and margination of chromatin; these nuclear inclusions are made more obvious by a clear unstained halo which is a shrinkage artifact produced by fixation (Fig. 5-3A).

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