Electron microscopic tracing of pathogenetic events in intestinal chlamydial infections of newborn calves

An Infectious Pig Model of Crohn's Disease

BACKGROUND

Over the last several years, we have demonstrated that intestinal lymphangitis and lymphatic obstruction are fundamental lesions in Crohn's disease, for which no therapy is currently available. There is an infectious enteritis of young pigs that offers an opportunity to understand how the lymphangitis of CD may have been initiated. The pathology of chlamydial enteritis was described earlier, from 1987 to 2009.

MATERIALS AND METHODS

Tissue blocks and hematoxylin and eosin-stained slides from Chlamydia suis-inoculated young pigs were provided by D. Rogers and F. Guscetti. Experimental animals, gnotobiotic and conventional, had been autopsied 4, 7, and 10 days postinoculation. Serial sections of intestine were immunostained with a Chlamydia trachomatis antibody, which cross-reacted with C. suis antigen, and compared with hematoxylin and eosin preparations.

RESULTS

Immunohistochemistry revealed antigen in villous epithelial cells of jejunum and ileum and in the endothelium of lacteals and lymphatics by day 4. This was accompanied by lymphatic endothelial necrosis, lymphangitis, and inflammatory lymphatic obstruction, through several layers of the affected intestinal segments, days 4 through 10.

CONCLUSIONS

Although the original authors documented lesions to define the porcine disease, here the author characterizes the lymphangitis as a model for understanding Crohn's disease and suggests a chlamydial origin for the latter.

Role of M cells and macrophages in the entrance of Mycobacterium paratuberculosis into domes of ileal Peyer's patches in calves

Ligated ileal loops of calves were inoculated with live and heat-killed Mycobacterium paratuberculosis and were examined by light and electron microscopy. At 5 hours after inoculation, acid-fast bacilli were in subepithelial macrophages, but not in M cells covering domes. At 20 hours, more than 50 acid-fast bacilli per cross section were in subepithelial macrophages in domes. Both living and heat-killed bacilli passed into domes. Addition of anti-M. paratuberculosis bovine serum to the inoculum enhanced entry of bacteria into domes. By electron microscopy, intact bacilli with electron-transparent zones (peribacillary spaces) were in the supranuclear cytoplasm of M cells at 20 hours. M cells also contained vacuoles, including electron-dense material interpreted as degraded bacilli. Subepithelial and intraepithelial macrophages contained bacilli and degraded bacterial material in phagosomes. These results suggest that calf ileal M cells take up bacilli, and that subepithelial and intraepithelial macrophages secondarily accept bacilli or bacterial debris which are expelled from M cells.

Pathogenesis of Brucella abortus in chicken embryos

Chicken embryos inoculated with Brucella abortus at 6, 10, and 12 days of incubation were examined by light and electron microscopy. B. abortus was identified by avidin-biotin immunoperoxidase and immunogold techniques. Death occurred from 2 to 5 days post-inoculation, depending on age of the embryo and route of inoculation. B. abortus was recovered from all infected eggs. Brucellae had spread throughout all tissues and localized preferentially within cells of mesodermal derivation. Organ distribution and degree of bacterial replication varied with age of the embryo at time of inoculation. In 6-day-old embryos, B. abortus localized preferentially in endoderm and mesoderm of yolk sac wall, extra- and intraembryonic serosal epithelia, and glomeruli of the mesonephros. In 10- and 12-day-old embryos, B. abortus spread to all tissues; renal glomeruli, liver, spleen, and heart were most severely infected. Intracellular B. abortus was within the rough endoplasmic reticulum of mesenchymal, mesothelial, yolk endodermal, and hepatic cells. In mononuclear phagocytes, endothelial cells, and granulocytes, bacteria were within membrane-bound vacuoles. Intracellular replication of B. abortus in embryonic tissues, especially yolk endoderm, closely resembled that in experimental infections of trophoblasts.

Pathogenesis of placentitis in the goat inoculated with Brucella abortus. II. Ultrastructural studies

Pregnant goats were inoculated intravenously or in uterine arteries with Brucella abortus, and tissues from the uterus and placenta were examined by electron microscopy. Identification of B. abortus in placentae was with antibody-coated colloidal gold. B. abortus was first seen in phagosomes of erythrophagocytic trophoblasts and in the rough endoplasmic reticulum of chorioallantoic trophoblasts. Subsequently, trophoblast necrosis and ulceration of chorioallantoic membranes were present. Coincidently, B. abortus was present in the lumen of placental capillaries. In late stages of infection, placental vasculitis was present, and placentomal trophoblasts were separated from maternal syncytial epithelium. In lesions with vasculitis, large numbers of B. abortus were in connective tissue of chorionic villi. Within the placentome, trophoblasts that lined chorionic villi contained no intracellular bacteria and were separated from B. abortus by intact basement membranes. These results suggest that bacteremic B. abortus is endocytosed by erythrophagocytic trophoblasts and that B. abortus replicates in the rough endoplasmic reticulum of chorioallantoic trophoblasts. Replication of brucellae in trophoblastic rough endoplasmic reticulum is unique; we believe that B. abortus may utilize endoplasmic reticulum for synthesis and glycosylation of bacterial membrane proteins or that B. abortus catabolizes trophoblast secretory proteins.

The ultrastructure of macrophages in granulomatous colitis of Boxer dogs

Thirteen cases of granulomatous colitis of Boxer dogs were studied by electron microscopy to define the contents of macrophages and to seek infectious agents. Macrophages were of three types. The most numerous were distended with residual bodies composed of membranes and parallel pairs of membranes, many arranged in circular patterns. A second common form had heterogeneous cytoplasm distended with phagosomes containing numerous small granular spheres of various sizes and electron densities. The least common were "young" macrophages containing phagocytic vacuoles. Rare macrophages in four of 13 dogs contained bacteria. Macrophages in five of the dogs contained abundant coccoid, coccobacillary of lobulated granular structures, 100-500 nm in diameter, resembling chlamydia. Transition from phagocytic particle to phagosome to residual body was apparent. Granulomatous colitis of Boxer dogs is probably caused by a lipid-rich, ribosome-rich, coccoid to coccobacillary organism that possesses a cell membrane and sometimes a nucleoid, and ranges from 100 to 500 nm in size.