Somatic diversification and affinity maturation of IgM and IgG anti-DNA antibodies in murine lupus

Molecular events occurring during the process of generation of pathogenic immunoglobulin (Ig)G anti-DNA antibodies in systemic lupus erythematosus (SLE) were studied using a newly established method. We analyzed the Ig variable (V) region gene sequence and DNA-binding activity of IgM and IgG anti-DNA monoclonal antibodies (mAb) from individual SLE-prone (NZB x NZW) F1 mice. The first event appeared to be clonal selection and expansion of IgM anti-DNA clones, in which several clones had intraclonal V gene mutations. Although the number of mutations was small, the mutated IgM clones were associated with an increase in DNA-binding activity. The somatic mutations located in complementarity-determining regions (CDR) and in framework regions (FR) of V genes were apparently related to changes in DNA-binding activity. IgG anti-DNA clones that progressively increased in number with aging had numerous somatic mutations in the V region genes and there was a pair of clones which showed an intraclonal accumulation of mutations, in association with increase in the DNA-binding activity. All these findings show that somatic mutations associated with affinity maturation of the V region begin immediately before isotype-switching from IgM to IgG of the clones that have been selected and expanded, in an antigen-driven manner and/or by other forces. We propose that further accumulations of intraclonal somatic hypermutation, in association with selection and expansion of high affinity IgG clones, may lead to formation of highly pathogenic anti-DNA antibodies.

[Lysosomes in the regulation of hormone secretion in the pituitary-adrenal gland axis]

The morphology and morphometrics of the lysosomes and associated structures were studied in hyposecreting corticotrophs and the cells of adrenal cortex zona fasciculata of the rats. Hyposecretion of this two types of the cells in the pituitary-adrenal gland axis was induced by dexamethasone administration. The lysosomes and other hydrolydase-positive structures were identified with CMPase cytochemistry. Quantitative evaluation of the lysosomes, crinophagic and autophagic vacuoles was carried out on the micrographs with MOP-Videoplan system. The results indicated that while inhibited secretion of ACTH accompanied by the increase of the crinophagic and autophagic vacuoles in corticotrophs, inhibited secretion of corticosterone accompanied by the increase of the autophagic vacuoles containing the mitochondria, ER which were steroid-synthesizing apparatus in adrenal cortex cells. The findings in the present study suggested that lysosomal degradation mechanism play a significant role in the regulation of hormone secretion in pituitary-adrenal gland axis. In addition to affirming earlier data that lysosomes took part in the regulation of protein secretion by crinophagy, the main conclusion derived from the present study was that lysosomes also functioned in the regulation of steroid secretion. By the way of autophagy i.e. sequesting and degrading a part of the steroid-synthesizing apparatus, the lysosomes rendered a mechanism in steroid-secreting cells to involve to the regulation process of hormone secretion. This might be an important and general rule as the crinophagy be to the protein-secreting cells.

[Leydig cells--a normal cell model of cellular autophagy]

In the present study, we tried to estimate, in a semiquantitative way, the relative frequency of the autophagic activity in various cell types under physiological condition. The results indicated that the highest activity appeared to be in the Leydig cells of rat testes. Autophagosomes were frequently observed in electron microscope photographs of Leydig cells, which provide a good model to study the autophagocytosis in normal cells. The autophagic process in Leydig cells was observed with the electron microscope in preparations treated to show CMPase activity. The mode of formation of autophagosomes in Leydig cells can be divided into three steps. Step 1, flattened membranous elements expand to enclose a small cytoplasmic territory to form pre-autophagosome. Step 2, The double membrane profile of the pre-autophagosome then completely encloses the cytoplasmic territory to form early autophagosome in which structurally normal organelles are contained. Step 3, the transformation of an early autophagosome into a late one is accompanied by the loss of one of the two delimiting membranes, the partial disintegration of the enclosed content and simultaneous acquisition of acid phosphatase activity. The enzymatic reactivity is acquired following a close association with the lysosomes. The late autophagosome then reaches the cell surface and appear to exocytose their residual content.

[Lysosomes in the regulation of hormone secretion in endocrine cells]

Enzyme cytochemistry and immunocytochemistry were utilized to study the morphological alterations of the lysosomes and associated crinophagic and autophagic structures in the hypo-secreting pituitary gonadotrophin and Leydig cells induced by exogenous androgen. The lysosomes and autophagic vacuoles in the electron micrographs were quantitatively analysed. The morphological and quantitative data led to the following conclusions: 1) The hypo-secreting gonadotrophin showed an increase in the number of lysosomes and an enhancement of crinophagy. It demonstrated once again that the lysosomes in the protein and polypeptide hormone secreting cells play a role in the regulation of secretion process by means of the crinophagy. 2) The hypo-secreting Leydig cells showed an increase in the number of lysosomes and an enhancement of autophagic activity. This indicated that the lysosomes in the steroid hormone secreting cells also function in the regulation of hormone secretion but by means of autophagy which scavenge a part of steroid-producing apparatus and hormone. The autophagy might have similar effect in regulation of steroid secretion to the crinophagy in regulation of protein secretion.

[Animal experiment studies of the toxicity of fluorodeoxyuridine (FUDR) and 5-fluorouracil (FU) within the scope of regional liver infusion chemotherapy]

In this study we examined the cytostatic compounds 5 FU and FUDR which are most frequently used in regional chemotherapy for any incidence of hepatobiliary toxicity in animals. For this we compared the intraarterial as well as the intraportal application. Differences between the treatment groups were found in the biliary extraction of these two cytostatic agents. The quantity of metabolites in the bile which could be proven by the MR-spectroscope was highest following intraarterial FUDR infusion, but strong deviations were found in individual cases. A correlation of these findings with the observed frequent hepatobiliary side effects could not be found. It could be shown that the rate and severity of chemical hepatitis and lymphocytic infiltrations in the periportal fields of the liver has no connection to either the cytostatic agent used nor the application form used. Although a sclerosing cholangitis could only be seen in intraarterial therapy. In these cases both cytostatic agents under observation were found to be responsible for this effect in the examined animals. The incidence of sclerosing cholangitis during regional chemotherapy of liver metastases with fluoridised pyrimidines seems to be contingent on multiple factors such as circulation disturbances in combination with drug toxicity.