Serological distinction between DR antigens and lymphocyte activating determinants

A computational study of somatostatin subtype-4 receptor agonist binding

The somatostatin subtype-4 receptor (sst4) is highly expressed in neocortical and hippocampal areas, which are affected by amyloid beta accumulation. Sst4 agonists enhance downstream activity of amyloid beta peptide catabolism through neprilysin and may slow the progression of Alzheimer’s disease (AD). Sst4 is a G protein coupled receptor (GPCR), the structure of which has yet to be resolved. A newly constructed sst4 homology model, along with a previously reported model-built sst4 receptor structure, were used in the present study to gain insights into binding requirements of sst4 agonists employing a set of compounds patented by Boehringer Ingelheim. Besides aiming at delineating binding at the macromolecular level of these recently disclosed compounds, our objectives included the generation of a quantitative structure-activity relationship (QSAR) global model to explore the relationship between chemical structure and affinity. Through the implementation of model building, docking, and QSAR, plausible correlations between structural properties and the binding affinity are established. This study sheds light on understanding binding requirements at the sst4 receptor.

Graphical abstract

Characterization of cell lines enhancing IL-2 production by human phytohemagglutinin-stimulated lymphocytes

Certain cell lines were found to significantly enhance IL-2 production by phytohemagglutinin-stimulated T lymphocytes, and the mechanisms involved in mediating such an enhancement have been studied. All B-lymphoblastoid cell lines (B-CL) tested had an enhancing capability, even lines which were immature, surface immunoglobulin negative, or negative for EBV-associated antigens or Fc receptors. Furthermore, a B-CL lacking HLA-A, B, and C, antigens as well as a HLA-DR-deficient mutant line enhanced IL-2 production. Autologous B-CL as well as allogeneic lines were able to augment IL-2 production. Cell lines from patients with T-cell acute lymphoblastic leukemia did not stimulate, while more mature, DR-positive T-cell lines did. Although all HLA-DR positive cell lines, regardless of their derivation, provided enhancement, several lines of evidence, including blocking experiments with anti-DR antibodies, indicated that the reaction was not HLA-DR mediated. The enhancing determinant(s) appeared to be cell associated since CL supernatants were ineffective, and it may serve as an important additional signal to the preactivated IL-2-producer T-cell.

Functional characteristics and differential expression of class II DR, DS, and SB antigens on human melanoma cell lines

Although most cultured melanoma cell lines express DR Class II molecules, many of these do not also express the DS (MB) Class II molecules as detected by a monoclonal antibody specific for DS. Cells lacking either DR or DS molecules or both could only be induced to express DR antigens in rare cases by combined incubations with azacytidine and Interleukin-2 conditioned medium, although the expression of DR molecules on fibroblasts or U937 monocytes could more easily be induced under the same culture conditions. Melanoma cells expressing DR antigens could function in antigen presentation for the histocompatibility antigens themselves and for DR specific presentation of TNP determinants to allogeneic T-cells sensitized to TNP modified lymphocytes and showing restriction in their responses to the specificity of the DR molecules expressed on the original, autologous sensitizing cells. DR positive melanoma cells could not, however, be demonstrated to function in the presentation of any of the soluble antigens tested. All DR positive melanoma cells also expressed SB antigens, but these were not detected on DR negative melanoma cells. These studies collectively indicate that the expression of Class II histocompatibility antigens on diverse cell types is subject to differential regulatory control and is associated with differences in their functional activities.