Cognitive features of continuous antigenic determinants

We sought to identify the features controlling the specificity of antibody recognition and thus gain insights into molecular recognition between proteins in general. A total of 103 epitopes within 63 well-defined antigenic peptides homologous with the relevant antigen sequence were identified. The contribution of each amino acid residue to the antibody binding activity of each epitope was investigated by ELISA testing of complete sets of peptide analogs containing single amino acid replacements. The data are summarized in a replaceability matrix. Some of the high frequency replaceabilities were expected, such as aspartate for glutamate, serine for threonine, etc., but unexpected relationships were also found, such as a high degree of acceptability of methionine as a replacement. Replaceability with a residue of opposite charge was rare. Glycine and tyrosine were frequently of low acceptability, except for glycine as a replacement for alanine. It was found that on average only about four to five amino acid residues in epitopes were required to determine specificity and provide binding energy. Specificity and binding energy were attributed to amino acid side chains rather than main chain atoms. Propensity factors for occurrence of amino acids in antigenic determinants were calculated. The prominence of certain hydrophobic residues as residues critical to recognition by antibody suggests that the molecular surface of an antigen in its combined form with antibody is altered from that occurring in the absence of antibody. Thus, antigenicity is not a static surface phenomenon but depends on the ability of the antigen to undergo rearrangement, supporting the induced fit concept.     

Degradation of ZAP-70 following antigenic stimulation in human T lymphocytes: role of calpain proteolytic pathway.

T cell activation by the specific Ag results in dramatic changes of the T cell phenotype that include a rapid and profound down-regulation and degradation of triggered TCRs. In this work, we investigated the fate of the TCR-associated ZAP-70 kinase in Ag-stimulated T cells. T cells stimulated by peptide-pulsed APCs undergo an Ag dose-dependent decrease of the total cellular content of ZAP-70, as detected by FACS analysis and confocal microscopy on fixed and permeabilized T cell-APC conjugates and by Western blot on total cell lysates. The time course of ZAP-70 consumption overlaps with that of zeta-chain degradation, indicating that ZAP-70 is degraded in parallel with TCR internalization and degradation. Pharmacological activation of protein kinase C (PKC) does not induce ZAP-70 degradation, which, on the contrary, requires activation of protein tyrosine kinases. Two lines of evidence indicate that the Ca2+-dependent cysteine protease calpain plays a major role in initiating ZAP-70 degradation: 1) treatment of T cells with cell-permeating inhibitors of calpain markedly reduces ZAP-70 degradation; 2) ZAP-70 is cleaved in vitro by calpain. Our results show that, in the course of T cell-APC cognate interaction, ZAP-70 is rapidly degraded via a calpain-dependent mechanism.     

Heterologous antigenic stimulation in induction of delayed hypersensitivity.

An influence of a delayed hypersensitive reaction to a primary antigen on the induction of delayed hypersensitivity to a second unrelated antigen was observed in guinea pigs immunized with azobenzenearsonate-N-acetyl-L-tyrosine (ABAT), and injected intradermally 3 weeks later with a mixture of ABAT and secondary antigen. Animals so treated developed delayed hypersensitivity to sheep red blood cells (SRBC) or Type II pneumococcal polysaccharide as secondary antigens, as measured by skin test reactivity and inhibition of macrophage migration, whereas ABAT unsensitized control groups did not. However, attempts to induce delayed reactivity to proteins as secondary antigens were unsuccessful. The injection of secondary antigen into a mineral oil-induced inflammatory lesion did not induce delayed hypersensitivity, suggesting that specific reactivity to ABAT is a prerequisite for heterologous induction. Possible mechanisms for the observed phenomenon, including a role for macrophages, are discussed.     

Ultrastructural features of supraspinal muscles in rabbits after long-term transcutaneous lateral electrical surface stimulation (LESS)

Lateral electrical surface stimulation is one of methods used in the therapy of the progressive form of idiopathic scoliosis (IS) in children and youth. However, there are data suggesting that this method may lead to serious adverse side effects, when used for a too long period of time per day. To clarify this issue, the present study was aimed at disclosing possible changes in the ultrastructural appearance of rabbit supraspinal muscles undergoing long-term stimulation (9 h per day, 3 months), an animal model successfully used to mimic the situation in humans. In comparison to the control animals, muscles of "overstimulated" rabbits exhibited clear signs of microscopical lesions, including depletion and disintegration of myofilaments, proliferation, dilatation and, sometimes, swelling of sarcoplasmic reticulum and/or mitochondria, as well as signs of destruction of the Z line. The above-mentioned abnormalities, especially the signs of degenerative processes associated with the Z line and the observed microlesions strongly suggest that the failure of the long-term LESS therapy of the IS may be attributable to these ultrastructural lesions.     

Spontaneous activity of hippocampal neurons and stimulation rhythm acquisition in young rabbits during learning: age features

Ontogenetic mechanisms of memory formation were studied using an experimental model of conditioned reflex to time, i.e., trace acquisition of a stimulation rhythm by hippocampal CA1 neurons of young (1-4 weeks old) and adult rabbits (5-6 months old). It was found that age-related development of learning ability includes several stages: complete absence of memory traces (6-7 days old), rapid acquisition without consolidation (8-14 days old), and formation of perfect memory (25-30 days old). Both specific and nonspecific changes in spontaneous activity of neurons were observed. Changes in the rate of discharges related to rhythmic stimulation were accompanied by changes in spontaneous activity. With the development of an animal, spike activity increased in parallel with improving of the functional properties of neurons, their structural organization, formation of the afferent contacts in the hippocampus completed after a period of three weeks from birth, and formation of metabolic processes, modulatory systems, and traffic function of hippocampal neurons. A capability for plastic reorganization is of great importance for adaptation mechanisms and conditioned behavior of a developing animal in accordance with structural maturation and development of the functional regulation of neuronal reactivity in the hippocampus.     

Mechanisms of T-lymphocyte stimulation of erythropoiesis under local body irradiation

Thymocytes transplanted into thymectomized mice with a locally irradiated lower limb in a dose of 7 Gy were accumulated in the depleted bone marrow to stimulate the processes of postradiation erythron regeneration. Cytosar treatment did not affect the regulatory function of thymocytes. At the same time thymocytes treated with actinomycin D possessed less powerful stimulating effect than intact ones.     

Cutting edge: immediate RANTES secretion by resting memory CD8 T cells following antigenic stimulation

The efficiency of CD8 memory response relies partially on the modification of cellular functional capacities. To identify effector functions that can be modified following priming, we have compared the chemokines produced by naive and memory CD8 T cells. Our results show that in contrast to naive cells, resting memory CD8 T cells contain high levels of RANTES mRNA. As a result, they have the capacity to rapidly secrete RANTES upon ex vivo antigenic stimulation. In contrast to that of IFN-gamma, RANTES secretion is mainly due to the translation of the pre-existing mRNA.