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Biomedical subjects

N R Cooper

Publications and source records attributed to N R Cooper.

At least 145 records · Page 8Linked to original sources
PubMed1973

Formation and function of a complex of the C3 proactivator with a protein from cobra venom.

The role of C3 proactivator (C3PA) and a factor isolated from cobra venom (CoF) in the formation of a principle able to cleave C3 was investigated. The results clearly demonstrate two modes of interaction of C3PA with CoF. In isolated form, C3PA and CoF were found to form a reversible protein-protein complex in free solution. This complex had some C3 cleaving activity. In the presence of minute amounts of a partially purified normal serum substance, factor D, the C3PA-CoF complex was stabilized and its efficiency in cleaving C3 was greatly increased. Factor D is thus an activator of C3PA. A firm complex composed of C3PA and CoF, and possessing C3 cleaving activity, was also formed by addition of CoF to serum.

Animals↗
PubMed1973

Interaction of histocompatibility (HL-A) antibodies and complement with synchronized human lymphoid cells in continuous culture.

The interaction of histocompatibility (HL-A) antibodies and complement with synchronized human lymphoid cells in continuous culture has been investigated. The sensitivity of cultured lymphoid cells to HL-A antibody-mediated lysis in the cytotoxic test, the extent of activation of the complement system, the degree to which labeled complement components are bound, and the ability of these cells to absorb HL-A alloantibodies do not vary significantly during the cell growth cycle. The constancy of histocompatibility antigen expression throughout the growth cycle of cultured cells suggests that these cell surface markers are an essential part of membrane cytoarchitecture and could well play a critical role in determining the normal function of the cell membrane.

Animals↗
PubMed1973

Activation of human complement by human lymphoid cells sensitized with histocompatibility alloantisera.

Cultured human lymphoid cells sensitized with human histocompatibility (HL-A) antibodies were able to activate the human complement system in vitro. Some HL-A alloantisera selectively activated the alternate complement pathway while other antisera activated only the classical pathway. A third group of alloantisera was equally able to initiate complement action by way of either pathway. The mechanism of complement activation did not correlate with the HL-A antigen present on the cells or the HL-A specificity of the alloantisera, indicating that the antigenic determinants or distribution on the cell surface play on direct role in selecting the pathway of activation. In this completely homologous system the alternate pathway was found to have the same cytolytic potential as the classical pathway. Thus, an altered or damaged membrane is not a prerequisite for the production of cytolytic damage by the alternate pathway. A complete understanding of the mechanism of interaction of membrane bound antigens and antibodies with the complement system may provide a versatile tool for the investigation of membrane antigen expression.

Antibody Specificity↗
PubMed1971

Cell cycle-dependent immune lysis of Moloney virus-transformed lymphocytes: presence of viral antigen, accessibility to antibody, and complement activation.

The expression of Moloney leukemia virus on the surface of a viral-induced lymphoma cell, availability of the virus to anti-viral antibody, and the nature and extent of activation of the complement system during the cell cycle were studied in vitro. Viral antigen was present on the cell surface, accessible to antibody, and was able to activate complement in the presence of antibody throughout all cellular growth phases, while cytotoxicity was confined to the G(1) phase of cell growth. In addition, when cells were arrested in metaphase, viral antigen could be demonstrated on the cell surface by immunofluorescence, and budding virus was seen by electron microscopy. All nine components of complement were activated on the addition of antibody throughout the cell cycle. Additional experiments indicated that in the presence of antibody, C3 and/or C4 were immunospecifically bound to viral-induced lymphoma cells throughout the cell cycle as a result of complement activation. These results indicate that the inability to lyse the cells in the presence of specific anti-viral antibody and complement during the logarithmic phase of cell growth is not due to the lack of expression of Moloney virus antigen(s) on the cell surface, inaccessibility of this surface antigen(s) to antibody, or failure to activate the complement effector system.

Animals↗
PubMed1970

The reaction mechanism of human C5 in immune hemolysis.

The data presented here indicate that the C5 reaction step may proceed via the specific attachment of C5 to EAC1,4,2,3 and the formation of a hemolytically active C5 intermediate complex. During this process only a minor proportion (less than 4%) of C5 offered to EAC1,4,2,3 becomes bound, although the remaining C5 also participates in the reaction as evidenced by its inactivation in the fluid phase. Once bound, C5 is exceptionally efficient in producing hemolysis, requiring less than seven specifically bound molecules per cell for the production of a hemolytic lesion. The extent of formation of the C5 intermediate complex is primarily dependent on the number of molecules of C4, 2 and C3 present on the cells employed for its generation. In these respects, the mode of action of C5 is completely analogous to that of the other components of complement thus far investigated. The C5 step differs, however, in other aspects. The binding of C5 is influenced by C6 and C7, components which are thought to act subsequent to it in the complement sequence. In addition, the hemolytic activity of the isolated C5 intermediate complex is exceedingly labile, having an average half-life at 30 degrees C of only 9 min. This characteristic distinguishes the C5 step, along with the C2 step, as potentially rate-limiting in the complement reaction. However, unlike C2, C5 remains firmly cell-bound during the decay process and apparently undergoes an alteration in situ which renders it hemolytically unreactive. Finally, C5 is unique in that it readily adsorbs in native form to unsensitized erythrocytes. This nonspecifically bound C5 remains firmly attached, although it may be specifically utilized as a source of C5 by an ongoing complement reaction. The significance of the marked affinity of native C5 for cell-surface receptors remains to be determined.

Adsorption↗
PubMed1969

Immune adherence by the fourth component of complement.

An immune complex becomes reactive in immune adherence after the specific binding of the fourth component of complement (C(4)). Immune adherence produced by the fourth component of complement is indistinguishable from classical immune adherence in terms of all parameters tested, except that it is entirely independent of the participation of the second and third components of complement.

Animals↗