Biomedical subjects
J B Lum
Publications and source records attributed to J B Lum.
Properties of a second epitope of the murine Fc receptor for aggregated IgG.
The murine macrophage and lymphocyte Fc receptor for aggregated IgG (Fc gamma R) has previously been characterized by using the anti-Fc gamma R monoclonal antibody (mAb), 2.4G2. In the studies presented here, we describe a new mAb, 6B7C, that defines a second epitope of the Fc gamma R. The tissue distribution of the 6B7C epitope is coincident with the 2.4G2 epitope. However, only the 2.4G2 epitope is accessible to mAb binding on intact primary macrophages or lymphocytes. The 6B7C epitope is not detectable on primary macrophages or lymphocytes but is exposed on a portion of B lymphocyte Fc gamma R after activation by lipopolysaccharide and on some tumor cell lines. The expression of the 6B7C epitope on the surface of B lymphoblasts and tumor cell lines seems to correlate with their ability to release soluble Fc gamma R. The 6B7C mAb has the advantage that it reacts with native as well as denatured receptor and therefore can be used for techniques such as immunoblotting.
Characterization, mapping, and expression of the human ceruloplasmin gene.
Ceruloplasmin (CP) is a copper-binding protein in vertebrate plasma. It is the product of an intragenic triplication and is composed of three homologous domains. Oligonucleotide probes constructed according to published amino acid sequences were used to identify cDNA clones encoding human CP. Two clones, CP-1 and CP-2, differed from each other by the presence or absence, respectively, of a deduced sequence of four amino acids. The two clones provided 81% of the sequence encoding CP. Comparison of the nucleotides of the three domains of the CP coding sequence revealed internal domain homology with identity of sequences ranging from 50.1% to 56%. The nucleotide sequence of CP-2 cDNa was compared to that of a homologous human protein, clotting factor VIII, and was found to be 48% identical overall. The CP gene was mapped to human chromosome 3 by somatic-cell-hybrid analysis and to 3q25 by in situ hybridization; however, sites of hybridization to DNA on other chromosomal sites suggested additional CP-like DNA sequences in the human genome. A DNA polymorphism was detected with CP cDNA after endonuclease digestion of human DNA by Pst I. CP mRNA was detected in human liver, macrophages, and lymphocytes by in situ histohybridization.
Transferrin synthesis by inducer T lymphocytes.
Transferrin (Tf) is a growth factor that transports iron in plasma. It is essential for proliferation of activated T lymphocytes. Previous studies have suggested that peripheral blood cells are capable of synthesizing Tf. Using in situ hybridization techniques and human Tf complementary DNAs as probes, peripheral blood cells have been examined for sites of Tf messenger RNA (mRNA) transcription. The studies described here demonstrate that Tf is synthesized by a specific subset of T lymphocytes, the T4+ inducer subset. T lymphocyte proliferation is dependent upon the presence of both interleukin 2 (IL-2) and Tf, even though resting cells do not possess receptors for either. The present studies indicate that during T cell activation, induction of IL-2 mRNA transcription and IL-2 receptor expression precede the transcription of Tf mRNA and expression of Tf receptors, respectively. These events in turn precede the initiation of DNA synthesis. Transferrin and its receptor appear to be involved in an autocrine pathway which is functionally linked to the IL-2/IL-2 receptor autocrine loop.
Medaka eggs as a model system for screening potential teratogens.
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