Search PubMed⌕ Search

Biomedical subjects

T A Springer

Publications and source records attributed to T A Springer.

336 records · Page 19Linked to original sources
PubMed1976

Detergent-soluble HLA antigens contain a hydrophilic region at the COOH-terminus and a penultimate hydrophobic region.

Purified, detergent-soluble HLA antigens (p44,12) are composed of a glycoprotein of molecular weight 44,000 (p44) and a peptide of molecular weight 12,000 (p12), beta2-microglobulin. Upon digestion with papain, p44,12 is converted to p39,12, then to p34,12, which retains antigenic activity. The NH2-terminal amino acid sequences of p34 and p44 are identical. p44, p39, and p34 were purified, and comparison of their amino acid compositions showed that the COOH-terminal peptide removed by the first papain cleavage is hydrophilic and contains cysteine that can be alkylated after mild reduction. The penultimate COOH-terminal peptide removed by the second papain cleavage is hydrophobic, and presumably anchors HLA antigens to the membrane. This correlates with the observation that p44,12 and p39,12 bind detergent, while p34,12 does not. The orientation and integration of HLA antigens in the lymphocyte membrane were thus defined, and the structure suggests that HLA antigens span the plasma membrane.

Amino Acid Sequence↗
PubMed1976

Ambiguity of the thymidine index.

The observed thymidine indices of seven experimental tumor lines are compared as a function of duration of emulsion exposure. The effects of dose level of tritiated thymidine and background threshold are also evaluated. The results indicate that an arbitrary high background threshold discriminates against "lightly" labeled cells at short periods of exposure but that the chosen threshold becomes less critical with longer exposure. The observed thymidine index increases with increasing duration of emulsion exposure but appears to approach a plateau for all tumor systems. The "thymidine index curves" are significantly different for each tumor. There is an inverse relationship between the dose of tritiated thymidine and the duration of exposure required to recognize the same fraction of cells as labeled in a given tumor. Similar experimental conditions do not necessarily guarantee a valid basis for comparison of observed thymidine indices among tumors.

Animals↗
PubMed1974

Partial purification of detergent-soluble HL-A antigen and its cleavage by papain.

HL-A antigen solubilized with the non-ionic detergent, Brij 99, has been purified to about 50% of homogeneity from a cultured human lymphoblast line. It consists of two nonidentical subunits of 44,000 and 12,000 molecular weight (MW). Upon papain proteolysis the 44,000 MW peptide is converted by at least two cleavages to a 34,000 MW peptide, but the 12,000 MW peptide appears to be unchanged. Concomitantly, the apparent molecular weight in gel filtration chromatography under nondenaturing conditions in the presence of Brij 99 is reduced from 460,000 to 45,000. HL-A molecules produced by direct papain proteolysis of membranes and by papain treatment of purified detergent-soluble HL-A are identical.

Animals↗
PubMedDate not supplied

Sequence homology of the LFA-1 and Mac-1 leukocyte adhesion glycoproteins and unexpected relation to leukocyte interferon.

Cell-surface adherence reactions are fundamental to the biology of lymphocytes, monocytes and granulocytes. The lymphocyte function-associated 1 (LFA-1) and macrophage 1 (Mac-1) glycoproteins mediate differing types of adhesion reactions on these cells. LFA-1 participates in T-lymphocyte and natural killer-cell adhesion to target cells, whereas the Mac-1 antigen is identical to the complement receptor type 3, which mediates adhesion of monocytes and granulocytes to C3bi-sensitized particles. Deficiency of these proteins, in a heritable disease, results in multiple adhesion-related leukocyte defects. LFA-1 and Mac-1 resemble one another in overall structure, having alpha-subunits of relative molecular mass (Mr) 180,000 and 170,000, respectively, which are non-covalently associated with beta-subunits of Mr 95,000 in alpha 1 beta 1 complexes. Peptide mapping and immunological cross-reactivity have shown that the beta-subunits are highly related if not identical, but have revealed no similarities between the alpha-subunits. Nonetheless, the shared beta-subunit suggested that LFA-1 and Mac-1 might be members of a protein family containing diversified but evolutionarily related alpha-subunits. Therefore, we examine here the structure of the alpha-subunits by N-terminal amino-acid sequencing. Sequence homology shows that the alpha-subunits are members of a novel leukocyte adhesion protein family, and suggests that their evolution occurred by gene duplication. A search for similarities to previously sequenced proteins reveals a further unexpected homology between LFA-1 and leukocyte (alpha) interferons.

Amino Acid Sequence↗
PubMedDate not supplied

Two antigen-independent adhesion pathways used by human cytotoxic T-cell clones.

Cell-cell adhesion is essential for many immunological functions, including interaction of cytotoxic T lymphocytes (CTLs) with their targets. We have explored CTL-target interactions using well-characterized cloned human CTLs. Conjugate formation between these CTLs and many antigen-negative targets is almost as efficient as with specific target cells, but does not lead to target-cell lysis. Thus, on specific target cells, adhesion by antigen-independent pathways may occur concurrently with or precede antigen recognition. The molecules LFA-1, CD2 (T11, LFA-2) and LFA-3 have been shown to be involved in human CTL conjugation with and lysis of specific target cells. Here we describe monoclonal antibody inhibition studies using individual monoclonal antibodies and mixes which demonstrate (1) that LFA-1, CD2 and LFA-3 are involved in antigen-independent conjugate formation; and (2) suggest that CD2 and LFA-3 are involved in one pathway and LFA-1 in another. We confirmed the existence of distinct pathways by the demonstration that LFA-1-dependent adhesion requires divalent cations and is temperature-sensitive whereas CD2- and LFA-3-dependent adhesion does not require divalent cations and is temperature-insensitive. Together with previous data, our studies suggest that CD2 on the effector interacts with LFA-3 as its ligand on targets.

Antibodies, Monoclonal↗
PubMedDate not supplied

The T lymphocyte glycoprotein CD2 binds the cell surface ligand LFA-3.

CD2 (known also as T11 (ref. 1), LFA-2 (ref. 2) and the erythrocyte rosette receptor (ref. 3] is a functionally important T lymphocyte surface glycoprotein of relative molecular mass 50,000 to 58,000 (Mr 50-58 K) which appears early in thymocyte ontogeny and is present on all mature T cells. Monoclonal antibodies to CD2 inhibit cytotoxic T-lymphocyte (CTL)-mediated killing by binding to the T lymphocyte and blocking adhesion to the target cell. Such antibodies also inhibit T helper cell responses including antigen-stimulated proliferation, interleukin-2 (IL-2) secretion, and IL-2 receptor expression. Certain combinations of monoclonal antibodies to CD2 epitopes trigger proliferation of peripheral blood T lymphocytes, cytotoxic effector function and expression of IL-2 receptors by thymocytes, resulting in thymocyte proliferation in the presence of exogenous IL-2 (ref. 11). These findings suggest that CD2 can function in signalling as well as being an adhesion molecule. To understand the role of CD2 in T-cell adhesion and activation, it is essential to define its natural ligand. Our previous observation that purified CD2 inhibits rosetting of T lymphocytes with sheep erythrocytes and can be absorbed by sheep erythrocytes suggested it also might bind with detectable affinity to human cells. We now report that CD2 binds to a cell-surface antigen known as lymphocyte function-associated antigen-3 (LFA-3) with high affinity, and can mediate adhesion of lymphoid cells via interaction with LFA-3.

Antibodies, Monoclonal↗
PubMedDate not supplied

Anchoring mechanisms for LFA-3 cell adhesion glycoprotein at membrane surface.

The manner in which a membrane protein is anchored to the lipid bilayer may have a profound influence on its function. Most cell surface membrane proteins are anchored by a membrane-spanning segment(s) of the polypeptide chain, but another type of anchor has been described for several proteins: a phosphatidyl inositol glycan moiety, attached to the protein C terminus. This type of linkage has been identified on membrane proteins involved in adhesion and transmembrane signalling and could be important in the execution of these functions. We report here that an immunologically important adhesion glycoprotein, lymphocyte function-associated antigen 3 (LFA-3), can be anchored to the membrane by both types of mechanism. These two distinct cell-surface forms of LFA-3 are derived from different biosynthetic precursors. The existence of a phosphatidyl-inositol-linked and a transmembrane anchored form of LFA-3 has important implications for adhesion and transmembrane signalling by LFA-3.

Animals↗