ORIGINAL ARTICLE: Levels of expression of complement regulatory proteins CD46, CD55 and CD59 on resting and activated human peripheral blood leucocytes

• Published in: Immunology 2006-12, Vol.119 (4), p.522-528
• Main Authors: Christmas, Stephen E, de la Mata Espinosa, Claudia T, Halliday, Deborah, Buxton, Cheryl A, Cummerson, Joanne A, Johnson, Peter M
• Format: Article
• Language: English
• ISSN: 0019-2805; 1365-2567
• DOI: 10.1111/j.1365-2567.2006.02467.x

The cell surface complement regulatory (CReg) proteins CD46, CD55 and CD59 are widely expressed on human lymphoid and non-lymphoid cells. This study aimed to compare systematically levels of CReg expression by different leucocyte subsets and to determine whether levels were increased following activation in vitro. Levels of each CReg protein were similar on freshly isolated monocytes and all major lymphocyte subsets, except that CD4 super(+) cells expressed significantly less CD46 than CD8 super(+) cells (P < 0.05) while the reverse was observed for CD55 (P < 0.02). CD56 super(+) cells, predominantly natural killer cells, expressed significantly lower levels of CD59 than T cells (P < 0.02). CD45RO super(+) cells had higher levels of surface CD46 and CD59, but lower levels of CD55, than CD45RO super(-) cells (P < 0.02); CD25 super(+) cells also expressed significantly less CD55 than CD25 super(-) cells (P < 0.002). Neutrophils expressed higher levels of CD59, but lower levels of CD55, than monocytes. Following activation with phytohaemagglutinin, CD46 was up-regulated on all leucocyte subsets with the exception of CD56 super(+) cells. Both CD55 and CD59 were also markedly up-regulated on monocytes, and CD55 expression was greater on CD8 super(+) than CD4 super(+) cells following activation (P < 0.02). Lipopolysaccharide treatment did not significantly alter B-cell expression of CReg proteins whereas CD55 and CD59, but not CD46, were significantly up-regulated on monocytes (P < 0.02). These observations that CReg proteins are up-regulated on certain activated leucocyte subsets indicate that levels would be increased following immune responses in vivo. This could enhance both protection against local complement activation at inflammatory sites and also the immunoregulatory properties of these leucocytes.