Diaminobenzidine cytochemistry in cryo-ultramicrotomy for the detection of peroxidases

Conditional ablation of macrophages disrupts ovarian vasculature

Macrophages are the most abundant immune cell within the ovary. Their dynamic distribution throughout the ovarian cycle and heterogenic array of functions suggest the involvement in various ovarian processes, but their functional role has yet to be fully established. The aim was to induce conditional macrophage ablation to elucidate the putative role of macrophages in maintaining the integrity of ovarian vasculature. Using the CD11b-diphtheria toxin receptor (DTR) mouse, in which expression of human DTR is under the control of the macrophage-specific promoter sequence CD11b, ovarian macrophages were specifically ablated in adult females by injections of diphtheria toxin (DT). CD11b-DTR mice were given DT treatment or vehicle and ovaries collected at 2, 8, 16, 24 and 48  h. Histochemical stains were employed to characterise morphological changes, immunohistochemistry for F4/80 to identify macrophages and the endothelial cell marker CD31 used to quantify vascular changes. In normal ovaries, macrophages were detected in corpora lutea and in the theca layer of healthy and atretic follicles. As macrophage ablation progressed, increasing amounts of ovarian haemorrhage were observed affecting both luteal and thecal tissue associated with significant endothelial cell depletion, increased erythrocyte accumulation and increased follicular atresia by 16  h. These events were followed by necrosis and profound structural damage. Changes were limited to the ovary, as DT treatment does not disrupt the vasculature of other tissues likely reflecting the unique cyclical nature of the ovarian vasculature and heterogeneity between macrophages within different tissues. These results show that macrophages play a critical role in maintaining ovarian vascular integrity.

Advances in ultrastructural postembedment localization of antigens in Epon sections with peroxidase labelled antibodies

Procedures for ultrastructural postembedment immunolocalization of antigens were investigated by use of the indirect peroxidase labelled antibody method. Results were compared with those obtained with the ultrastructural preembedment technique. IgG globulins in IgG synthesizing cells of rat lymph nodes served as model. Formaldehyde fixation, ethanol dehydration and embedment in Epon 812 did not abolish immunoreactivity. Sufficient numbers of antigens remained for subsequent postembedment immunohistology. Antigen binding sites were readily localized in ultrathin sections. For this purpose, polymerized resin had to be partially removed. Sodium methoxide in methanol/benzene mixture rapidly dissolved ultrathin sections. Diluted alcoholic sodium hydroxide enabled reliable resin etching and subsequent immunostaining. Treatment of ultrathin sections with hydrogen peroxide alone, did not permit immunolocalization of IgG. Optimal antigen detection was attained with antibodies isolated by affinity chromatography and purified peroxidase conjugates. IgG was stained in the rough-surfaced endoplasmic reticulum, the perinuclear space and the Golgi apparatus; the subcellular distribution corresponded to that obtained with preembedment immunohistology. In the latter technique, substrate accumulation was more homogenous than in postembedment staining.