LFA‐1 β‐chain synthesis and degradation in patients with leukocyte‐adhesive proteins deficiency

Abstract

The defective membrane expression of the adhesive protein family (LFA-1, Mo1 and p150,93) on leukocytes from certain patients with recurrent bacterial infections was shown to be secondary to the absence of synthesis of mature beta chain that is common to all three antigens (Springer et al., 1984, Lisowska-Grospierre et al., 1986). In all patients, studies of beta-chain biosynthesis that lead to this conclusion were performed using the monoclonal anti-beta chain antibody to isolate the beta subunit. Since this antibody detects the mature form of beta chain only, the potential presence of a precursor or of an abnormal beta chain in the patient's cells could not be tested. The availability of the polyclonal antibody to the purified beta subunit allowed us to re-examine the biosynthesis of the LFA-1 subunits in 3 affected children. In all 3 patients, the absence of membrane expression of the LFA-1, CR3 and p150,95 proteins was confirmed. The LFA-1 alpha-chain precursor of 170 kDa was detected in the lysates of PHA blasts of two children, but was not detected in the third. The beta-chain precursor of 85 kDa was isolated by the polyclonal anti-beta chain antiserum from the cytoplasm of phytohemagglutinin and Epstein-Barr virus-induced blasts of one patient. The same antibody precipitated some peptides of smaller mol. wt. from the cell lysates of 2 other patients. These results suggest that in this disorder the membrane nonexpression of the adhesive proteins is probably due to the structural abnormality of beta chain which, although synthesized, is rapidly degradated.

CD4+ T Cell-Associated Pathophysiology Critically Depends on CD18 Gene Dose Effects in a Murine Model of Psoriasis

“…This conclusion is at least partly supported by our findings that the expression levels of all four possible ␣ subunits differed only in quantity, according to the reduction in total levels of ␤ 2 integrin heterodimers, when compared with CD18 wild-type leukocytes; and also by previously published results derived from studies on patients suffering from LAD1 (49,50,64,65). These authors stated that deficiency in ␤ 2 -integrin heterodimers appears to be quantitative rather than qualitative, with two patients expressing ϳ0.5% and one patient 5% of normal amounts of CD18.…”

“…1A). Evidence for a defective association between ␤ 2 integrin ␣-and ␤ 2 -chains potentially caused by a qualitative alteration in the CD18 hypo molecule was not supported by our data, as a deficiency in dimerization will normally lead to internalization of either subunit and, thereby, to a loss of cell surface expression (49,50).…”

Transfection of cells from patients with leukocyte adhesion deficiency with an integrin beta subunit (CD18) restores lymphocyte function-associated antigen-1 expression and function.

“…Association of the a subunit precursor with the (3 subunit precursor is necessary for additional carbohydrate processing and transport to the cell surface. Association with an a subunit was not detectable in any of the LAD patients who synthesize a A subunit precursor (7)(8)(9). After the isolation of cDNA clones encoding the (3 subunit of the leukocyte integrins (10, I 1) it was demonstrated that heterogeneous mutations in the common d subunit give rise to LAD (8,12).…”

“…One class of mutation results in no detectable mRNA or protein precursor, while a fourth class of mutation is characterized by the synthesis of trace amounts of ( subunit precursor and low levels of message (8,12). A fifth class of mutation results in synthesis of a (3 subunit that appears normal by SDS-PAGE, but fails to associate with the a subunit (8,9,12,13). This class of mutation could be due to point mutations in a or (3, or could affect a third protein required for their assembly.…”

A 19-year-old man with leucocyte adhesion deficiency. In vitro and in vivo studies of leucocyte function

“…mRNA was detected by Northern blotting using a CDI18 gene probe in our patient, as might be expected. A range of abnormalities of the P chain at the mRNA level has been described (Dana et al, 1987;Dimanche et al, 1987;Kishimoto et al, 1987). The detailed molecular pathology in our patient is currently being studied.…”