Human and murine lymphotoxins as a multicomponent system: progress in purification of the human alpha L component

The presence of antibodies to lymphotoxin and tumor necrosis factor in normal serum

Lymphotoxin (LT) and tumor necrosis factor (TNF) are cytokines that probably play a role in several autoimmune diseases. In this report, we describe the detection, in normal nonimmune serum, of naturally occurring antibodies that bind to recombinant human LT and TNF. The naturally occurring antibodies that bind to LT and TNF could explain why normal immunoglobulin is effective therapy in idiopathic thrombocytopenic purpura and Kawasaki syndrome.

Biotechnological production and functional characterization of leukocytic cytokine(s) with cytotoxic effect on resting but not activated thymocytes

In the present report we describe the analysis of suppressive and cytotoxic factor(s) derived from Con A-induced porcine leukocyte culture supernatant solution(s) (PCAS). The supernatant solution(s) had been produced on a biotechnological scale using porcine peripheral blood leukocytes isolated from 200 to 1000 1 of porcine blood. The supernatant solution(s) were tested for their effect during murine T cell activation. We found that crude supernatant solution(s) contain suppressive and cytotoxic factor(s) (SF) which have a similar selectivity for non-activated thymocytes as suppressive factor(s) previously detected in the supernatant solution(s) of allo-antigen-stimulated murine spleen cell cultures. SF was obtained from crude serum-free culture supernatants by fractionated ammonium-sulphate precipitation between 35 and 45% saturation. SF has the following characteristics: its release into the culture supernatant is dependent on mitogenic stimulation, it acts during early stages of T lymphocytic activation, the activity towards naive thymocytes is most likely caused by an irreversible cytolytic mechanism, and phenotypically and functionally immature thymocytes are preferentially affected through exposure to SF.

Isolation and identification of an alpha 2 subclass lymphotoxin (LT) subunit from the high-molecular-weight (complex) human LT class

The high-molecular-weight (MW) complex class (MW = greater than or equal to 200,000) of lymphotoxin (LT) may be involved in the process of lymphocyte-mediated cytolysis. This LT class was produced by concanavalin A-stimulated human adenoid and tonsil lymphocytes in vitro and purified approximately 1000 fold by a scheme employing lectin affinity chromatography on concanavalin A-Sepharose, negative hydrophobic affinity chromatography on phenyl-Sepharose, and molecular sieving on Ultrogel AcA 44. A cell-lytic subunit, termed C-alpha toxin, was dissociated from this partially purified complex LT (Cx) preparation. The identification of C-alpha toxin as an alpha 2 LT form was established by its comigration with the alpha 2 LT form during native polyacrylamide gel electrophoresis (PAGE), molecular sieving, and isoelectricfocusing. In addition, C-alpha toxin was neutralized by antiserum raised against purified alpha 2 LT, and the latter was neutralized by antiserum raised against C-alpha toxin. Furthermore, preliminary evidence indicates that both alpha 2 LT and C-alpha toxin are composed of peptides with apparent MW of approximately 69,000. Additional data indicate the Cx LT form is composed of alpha 2 LT and other subunits.

Lymphotoxins - a multicomponent system of growth inhibitory and cell-lytic glycoproteins

Activated lymphocytes from experimental animals and man can release materials, termed lymphotoxins , which cause growth inhibition and cell lysis in vitro. These molecules, from human lymphocytes, are glycoproteins which can be divided into five molecular weight classes. These forms are heterogeneous, for each MW class can be further subdivided into multiple charge subclasses. It is now clear certain MW classes are interrelated and form a system of cell toxins. The larger classes (greater than 140,000 d) are associated with nonclassical antigen-binding receptors (R), which can be of T cell origin. The smaller forms (less than 90,000 d) do not express R function and are derived from the larger forms, possibly by enzymatic action. Two MW classes, one receptor-associated and one non-receptor associated, have been purified to homogeneity and their peptide composition is being studied. Functional studies reveal the larger MW forms derived from alloimmune cell populations; can induce selective and nonselective destruction of cells in vitro. Antibodies which inhibit the in vitro cell lytic ability of various human LT forms can block different classes of human lymphocyte cell killing reactions in vitro.

The use of protein A in solid-phase binding assays: a comparison of four radioiodination techniques

Preparations of protein A radioiodinated by 4 different methods have been compared in indirect radioimmunoassays. The oxidative methods (chloramine-T and iodogen) for direct iodination of tyrosyl and histidyl residues were applied with high efficiency and gave a suitable product, provided the substitution ratio was kept low (1 iodine atom/molecule of protein A). Higher levels of modification tended to perturb the Fc-binding characteristics of the protein, especially with the use of iodogen. Introduction of the isotope via substitution of lysyl residues (Bolton-Hunter and Wood reagents) was also examined. The Bolton-Hunter modification of protein A gave an unsuitably low labeling efficiency; in contrast, the Wood reagent gave efficiencies approaching 50%. Protein A could be extensively substituted with the latter reagent (greater than 5 diiodinated benzimidate molecules per protein molecule). Thus, the use of the Wood-labeled protein A could raise the sensitivity of the binding assay at least an order of magnitude compared to using protein A iodinated by the oxidative methods. The effects on the biological activity of protein A exerted by the different labeling procedures are rationalized on the basis of the amino acid composition and tertiary structure of the protein.

Lymphotoxin cytotoxicity, a combination of cytolytic and cytostatic cellular responses

Guinea pig lymphotoxin inhibits the growth of mouse alpha L929 and guinea pig 104C1 tumor cells with lethal doses (LD 50's) of 0.4 and 200 units lymphotoxin/ml, respectively, in a colony inhibition assay. Refeeding with lymphotoxin-free medium is followed by resumption of 104C1 but not alpha L929 cell growth. This suggests that growth inhibition of alpha L929 is primarily due to cytolytic mechanisms, while that of 104C1 cells is due to cytostatic mechanisms. This is confirmed by radionuclide (3H, 51Cr, and 75Se) release assays with LD 50's of 1.0, 1.9, and 2.4 units lymphotoxin/ml, respectively, for alpha L929 cells, whereas as many as 100 units lymphotoxin/ml produce no radionuclide release from 104C1 cells. The L cell variant L929M is 10-fold more resistant to lymphotoxin colony inhibitory activity and 40-300-fold more resistant to cytolytic lymphotoxin activity as measured by the three radionuclide release assays than are alpha L929 cells. L929 and 2071 L cell variants are more resistant as a result of smaller cytolytic and cytostatic responses and some tumor cells, such as one strain of L1210 mouse leukemia cells, exhibit no detectable cytolytic or cytostatic responses to 100 units of guinea pig lymphotoxin. These observations demonstrate that the divergent susceptibilities of different cells to lymphotoxin result in part from constitutive variations in cellular cytolytic and reversible cytostatic responses to lymphotoxin.