Biotechnological aspects of antibody production in E. coli

The production of genetically engineered antibodies in Escherichia coli is now possible. The resulting fragments are completely functional and have antigen binding constants industinguishable from the natural antibody. This article summarizes the biochemical basis of this newly developed technology and the properties of the resulting fragments. It is likely that this technology will have an important role in antibody production for technical, medical and research uses. Screening of E. coli libraries may mount a challenge to traditional antibody production methods.     

Affinity requirements for induction of sequential phases of human B cell activation by membrane IgM-cross-linking ligands

The affinity of Ag interaction with a B cell's membrane IgM (mIgM) receptors has long been considered to play a critical role in the in vivo clonal selection of B lymphocytes. This study has examined a possible basis for this affinity selection at the level of Ag induction of sequential B cell activation phenomena, i.e., elevated membrane class II MHC expression (G0* excitation), G1 entry, and S phase entry. Functional experiments with model bivalent Ag, i.e., a group of murine mAb of diverse intrinsic binding affinities for human IgM, revealed that the minimal affinity requisites for inducing the above phenomena vary significantly. At a ligand concentration of 100 micrograms/ml, the induction of increased class II MHC expression, G1 entry, and S phase had minimal affinity thresholds of Ka approximately 0.2 to 2 x 10(6) M-1; approximately 7 x 10(6) M-1; and approximately 1 x 10(8) M-1, respectively. Pulsing studies revealed that whereas high affinity ligand was essential at later periods in the prolonged (greater than 24 h) signaling period that leads to S phase entry, mAb with significantly lower affinity were competent at signaling during the first 24 h. Because all but the lowest affinity ligand (Ka = 2 x 10(5) M-1) could effectively modulate mIgM, and furthermore, because B cells show a substantial increase in surface area during activation, it appears likely that one factor contributing to the higher affinity requirements for induction of late activation phenomena is a progressive decrease in the density of mIgM on the responsive B cells. These studies suggest that whereas only a small proportion of B cells, i.e., those with relatively high affinity for an antigenic epitope, will be triggered to clonally expand on encountering a paucivalent Ag in the absence of T cell help, a much wider spectrum of the B cell repertoire will be triggered to a state of partial activation. How the presence of ancillary T cells and cytokines may facilitate the full clonal expansion of these latter cells is discussed.     

Variations in thymocyte susceptibility to clonal deletion during ontogeny. Implications for neonatal tolerance.

Activation of immature thymocytes via the TCR results in programmed cell death and clonal deletion. We have examined thymocytes from mice of different ages and observed that, whereas TCR-mediated signaling caused deletion of thymocytes from newborn and 3-week-old mice, it failed to delete thymocytes from mice of 1 week of age. This could not be attributed to differences in cell surface TCR expression, TCR-mediated phosphoinositide hydrolysis or Ca2+ mobilization, or total cellular levels of TCR zeta- and eta-chains. Moreover, thymocytes of all ages were equally susceptible to corticosteroid- and Ca2+ ionophore-induced programmed cell death. These data are consistent with the notion that fetal and neonatal thymocytes represent a relatively synchronous wave of cells passing through phases in which they are susceptible and then resistant to TCR-induced programmed cell death. They also support the notion that the classical phenomenon of neonatal tolerance is due to clonal deletion and that the inability of allogeneic cells to tolerize mice at 1 week of age is because the thymocytes are refractory to TCR-alpha beta-mediated clonal deletion.     

Phytoplankton composition and spatial distribution of copper and zinc in the Fal Estuary (Cornwall,UK)

In the estuaries near Falmouth (Cornwall, UK) levels of dissolved copper and zinc are high, due to drainage of copper and tin mines. Phytoplankton species composition in the autumn of 1989 deviated in the metal-contaminated Restronguet Creek from that in other estuarine branches,viz. Fal, Tresillian and Percuil. In the riverine part of Restronguet Creek (Carnon River)Euglena mutabilis, known as an acidophilic (pH 3) metal-resistant flagellate, occurred at micromolar Cu and Zn, whereas in the clean riversChlamydomonas sp. andOocystis sp. occurred at nanomolar Cu and Zn. An ordination analysis revealed the following patterns in Cu, Zn and phytoplankton species composition in the poly- and euhaline waters. Seston-bound Zn and dissolved Zn were in equilibrium,Katodinium rotundatum is Zn-tolerant, andSkeletonema costatum occurred in water with high contents of Cu in seston. However, none of the variables in these patterns correlated at a significant level (p>0.05). The results show that algae-metal interactions are complicated, and that statistical correlations foundin situ need experimental verification.Communication no. 542 of the Delta Institute for Hydrobiological Research.     

Phospholipase A2 activity in human platelets. Isolation and purification of the enzyme

The activity of phospholipase A2 in blood platelets of healthy donors and IHD patients was examined. The enzyme activity was found to be increased 3-fold in platelets possessing a high level of functional activity (IHD) and by one order of magnitude in patients with myocardial infarction as compared with healthy donors. An enzyme preparation possessing a phospholipase activity was isolated from platelets by using salt extraction (KCl) and sonication. Purification of the enzyme by affinity chromatography resulted in two protein peaks both having a phospholipase A2 activity, the purification and molecular masses of these fractions being 768- and 2200-fold, and 13.5 and 15 kDa, respectively. It was supposed that these proteins are substrate-specific forms of phospholipase A2.     

RNA polymerase heterogeneity in Streptomyces aureofaciens: characterization by antibody-linked polymerase assay

The ability of Escherichia coli with different receptor specificities to interact with meconium was studied. E. coli strains expressing P-fimbriae, specific for Gal alpha 1-4Gal beta-containing receptors, were agglutinated by meconium at high titres. This reaction was inhibited by globotetraosylceramide. The attachment of P-fimbriated E. coli to human colonic epithelial cells of the HT-29 cell line was inhibited by meconium. Some type 1 fimbriated strains were agglutinated by meconium, but the agglutination was rarely blocked by methyl alpha-D-mannoside. The attachment by type 1 fimbriated strains to HT-29 cells was reduced by meconium only in some cases. These results suggest that meconium interacts with the P-fimbriae of E. coli, in a way that may influence bacterial colonization of the neonatal intestine.