Abstract: The inventors herein disclose new heterobifunctional chromophores that are capable of coupling with two distinct moieties. One moiety may be either a signal-enhancing agent or a blocking agent. The second moiety may be one member of a specific binding pair. The invention is based in part on the surprising result that when a chromophore is used as a "cross-linker" between a signal-enhancing agent and a member of a binding pair (essentially being buried between the two), the signal of the chromophore is not quenched. This arrangement, wherein the chromophore acts simultaneously as a cross-linker and a detectable compound, provides significant advantages over previously known compounds since the chromophore is sterically hindered from interacting non-specifically with substances present in the test systems. Moreover, the chromophore can be used as a cross-linker with little or no loss of detectable signal.

Abstract: The present invention demonstrates that M-CSF responsiveness and the M-CSFR expression can be used to discriminate monocytic and granulocytic cells within a population of cells which strongly expresses the CD34 antigen (CD34.sup.hi). Briefly, the method comprises isolating phenotypically and functionally defined CD34.sup.+ subsets, and staining with anti-M-CSFR monoclonal antibodies to measure expression on these primitive progenitors and cells committed to the granulocytic and monocytic lineages, based upon expression of M-CSFR. CD34.sup.hi M-CSFR.sup.hi cells are highly clonogenic and approximately 70% of the colonies are CFU-M (monocytic), whereas less than 20% were CFU-G (granulocytic). In contrast, CD34.sup.hi cells that were positive for the granulo-monocytic marker CD64 and negative for the M-CSFR contained high frequencies of 91% pure CFU-Gs. After 60 h in culture, CD34.sup.hi M-CSFR.sup.hi cells developed into distinct populations of M-CSFR.sup.hi and M-CSFR.sup.lo cells.