Attachment of Cell Walls of Chlamydia psittaci to Mouse Fibroblasts (L Cells)

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Abstract
14 C-labeled cell walls of the 6BC strain of Chlamydia psittaci , prepared from intrinsically labeled chlamydial cells by digestion with deoxycholate and trypsin, associated with mouse fibroblasts (L cells) in a manner comparable to that of intact C. psittaci. Almost half of the host cell-associated cell walls were not dissociated by trypsin, suggesting that they had been attached and then ingested. The attachment of cell walls to L cells was inhibited by a number of treatments known to block association of intact C. psittaci with L cells: heating the cell walls for 3 min or reacting them with antiserum against intact C. psittaci , or pretreating the L cells with trypsin or wheat germ agglutinin. Unlike intact cells of C. psittaci , cell walls were not immediately toxic for L cells, and they did not measurably adsorb neutralizing antibody. As revealed by making cell walls from intact C. psittaci labeled with 125 I by lactoperoxidase-catalyzed iodination, cell walls contained a much smaller number of surface-labeled proteins than did whole chlamydial cells. The most abundant surface-labeled protein was one with an apparent molecular weight of 43,000. In the final step of cell wall preparation, tryptic digestion of deoxycholate-extracted cells, this major surface protein was partially cleaved to a 40,000-dalton product. When the major surface protein (both the 43,000- and 40,000-dalton moieties) was electrophoretically separated from the other cell wall proteins and used to immunize a rabbit, antibodies that neutralized the infectivity of intact C. psittaci were elicited. It was concluded that cell walls retain the ability to associate with L cells in much the same way as do intact cells of C. psittaci , but, despite the simpler structure of cell walls, the element that binds C. psittaci to host cells cannot yet be identified.