C3b Receptors (CR1) on Peripheral Human Blood Cells

Holme, Elizabeth R (1986) C3b Receptors (CR1) on Peripheral Human Blood Cells. PhD thesis, University of Glasgow.

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CR1 is the receptor for the activated third component of complement C3b. It is present on the cell membranes of human erythrocytes, lymphocytes, polymorphonuclear leucocytes, mononuclear phagocytes, mast cells, B lymphocytes, some T lymphocytes and kidney podocytes. Purification of CR1 from human erythrocytes using cation exchange and affinity chromatography revealed a single protein with a molecular weight of 230000 daltons. This protein was used to raise a polyclonal antiserum in rabbits, which was then utilised in the development of a radioimmunoassay to quantitate the number of CR1 on human peripheral blood cells. This assay was used successfully to quantitate CR1 levels on erythrocytes. However, it could not be adapted to assess CR1 levels on monocytes, lymphocytes or polymorphonuclear leucocytes . CR1 levels have previously been reported to be reduced on erythrocytes from patients with systemic lupus erythematosus (SLE). However, there has been no agreement in the literature as to whether the reduced erythrocyte CR1 levels observed are acquired as a consequence of the pathological process of the disease or are an inherited defect. The aim of the experiments performed in this thesis was to establish whether CR1 levels are inherited or acquired. To examine this erythrocyte CR1 levels were studied in normal individuals and SLE patients. In addition, patients with rheumatoid arthritis (RA) were investigated. Serial studies were performed on normal individuals, SLE and RA patients to see whether there were temporal changes in CR1 levels. CR1 levels were also assessed in normal families and in families where one or more individuals had SLE to ascertain whether receptor levels were inherited. CR1 levels were quantitated using a radioimmunoassay, which measured the amount of 125I-F(ab')2 anti-CR1 binding to the erythrocytes. From this the number of binding sites per erythrocyte for the F(ab')2 anti-CR1 moiety was calculated (CR1 sites/erythrocyte). Seventy normal erythrocyte specimens were studied; the mean was 3320 CR1 sites/erythrocyte (range 0 to 21692 CR1 sites/ erythrocyte) whilst the mean for the SLE patients was 1541 (n=41, range 0 to 15766 CR1 sites/erythrocyte), significantly lower (p 0. 001) than the normals. Likewise the mean (1410 CR1 sites/erythrocyte, n=25) for the RA patients was also significantly lower (p <0.05). A striking observation was that many of the SLE patients had no receptors (27% as opposed to 1.5% in the normals and 0% in the RA group). When the SLE patients were further subdivided into those who were in an active disease phase or an inactive disease phase, the majority of patients with zero receptors were in an active disease state. When analysed further the mean CR1 level for the patients with active disease (356 CR1 sites/erythrocyte) was significantly lower (p <0.001) than those with inactive disease (2428 CR1 sites/erythrocyte). These levels were not related to any of the serological parameters studied. Serial studies on SLE patients showed that in some individuals the CR1 levels varied with disease activity, decreasing during exacerbations and increasing during remission. Family studies showed a clustering of low, medium or high CR1 levels in individual families. However, where a member of a family had SLE their CR1 levels were not akin to their families suggesting acquisition and not inheritance. Studies of two sets of identical twins showed that they did not have identical CR1 suggesting that they had acquired different levels. Two main conclusions may be drawn from these studies; firstly, genetic factors probably do influence CR1 levels as supported by the clustering of CR1 levels in the families studied and secondly, in some patients with SLE the CR1 levels were acquired, as indicated by the change in CR1 levels with disease activity and the lower levels found in patients with disease exacerbations. Two possible explanations could account for the acquisition of reduced receptor levels, receptor removal or receptor blockade. In support of the latter it was observed that large opsonized immune complexes (formed with thyroglobulin or DNA, with specific antiserum) bound to and totally or partially blocked the erythrocyte CR1. Thus in vivo blockade of CR1 by circulating immune complexes could account for the reduced CR1 levels seen in some SLE patients when their disease is in exacerbation.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Medicine, Cellular biology
Date of Award: 1986
Depositing User: Enlighten Team
Unique ID: glathesis:1986-77346
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jan 2020 09:11
Last Modified: 14 Jan 2020 09:11
URI: https://theses.gla.ac.uk/id/eprint/77346

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