Modulation of adhesion molecule CD54 expression on CD34+ hematopoietic progenitors.

Multiple cellular adhesion molecules are constitutively expressed on hematopoietic progenitors. CD54 (ICAM-1), a member of the immunoglobulin supergene family, has recently been shown to be present on a subset of hematopoietic progenitors. To demonstrate that this adhesion molecule is expressed on the surface of the hematopoietic progenitor following induction rather than in its basal state, we studied the expression of cell surface CD54 on flow-cytometric (FACS) gated progenitors (CD34+; lymph plus blast light scatter). A mean +/- standard deviation (SD) of 2.75 +/- 2.10% was seen for FACS-gated progenitors from freshly isolated bone marrow mononuclear cells (BMMNC) stained with anti-CD54 MAb. Following incubation at 37 degrees C for 20 to 22 hours in media supplemented with heat-inactivated bovine fetal serum (FBS), the percentage of FACS-gated progenitors staining with anti-CD54 MAb increased to 46.28 +/- 18.38. This increase was temperature and time dependent. The percentage of FACS-gated progenitors stained with anti-CD54 MAb did not increase following 20 to 22 hours of incubation at 4 degrees C. Furthermore, a subpopulation of FACS-gated progenitors staining with anti-CD54 MAb was detectable by 5 hours of incubation at 37 degrees C; the percentage of these progenitors staining with anti-CD54 MAb plateaued after 10 hours of timed incubation. Once induced, progenitor cell surface CD54 antigen density remained stable, as evidenced by a constant mean fluorescence intensity of anti-CD54 MAb staining. Three-color immunofluorescent studies showed that induction of CD54 occurred on CD45+ FACS-gated progenitors and that CD54 was induced on a subset of BMMNC expressing CD34 and CD11a, a counter receptor for CD54 that is limited in distribution to leukocytes. CD54 expression was induced to the same degree on FACS-gated progenitors positive or negative for CD19, CD36, and HLA-DR, respectively. These data indicate that CD54 is a unique adhesion molecule as its expression can be induced on CD34+ hematopoietic progenitors, and this induction does not appear to be related to hematopoietic progenitor lineage commitment or maturity.