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Biomedical subjects

A M Lawn

Publications and source records attributed to A M Lawn.

At least 19 recordsLinked to original sources
PubMed1988

Lymphocytes of the intestinal mucosa of chickens.

Examination, by light and electron microscopy, of the morphology and the staining properties of intraepithelial lymphocytes from the intestine of the chicken revealed a population of lymphoid cells, of which a proportion (up to 20%) is granulated. The majority of cells were immunoreactive with anti-T cell serum and can therefore be considered to be related to T-lymphocytes, but they did not proliferate when cultured with phytohaemagglutinin. The granulated cells were identical to those previously designated globule-containing leukocytes, but were distinct from mast cells in their morphology, staining reactions and the stability of the granules in different fixatives and buffers.

Animals↗
PubMed1984

The effect of immunity on the early events in the life-cycle of Eimeria tenella in the caecal mucosa of the chicken.

A comparison was made between the early events (asexual stages) in the life-cycle of Eimeria tenella in specifically immunized and control chickens. Particular attention was paid to the quantitative aspects and to the transport of sporozoites within intra-epithelial lymphocytes (IEL) from the enterocytes of the surface epithelium to the enterocytes of the crypts. There was a moderate decrease in the number of parasites initially seen in the mucosa of the immune birds, suggesting that some of the effects of immunity are exerted before penetration of the surface enterocytes, but the reduction in the numbers of developing parasites was more marked. This latter effect was due, at least partly, to failure of transfer of sporozoites from IELs to crypt enterocytes. These findings are discussed in relation to the efficacy of the immunity induced.

Animals↗
PubMed1983

Invasion of chicken caecal and intestinal lamina propria by crypt epithelial cells infected with coccidia.

The development of second generation schizonts of Eimeria necatrix and E. tenella was studied with the electron microscope. Invasion of the crypt epithelial cells by merozoites of the first generation schizonts caused changes in the morphology of the infected cells and stimulated their migration into the lamina propria through breaks which appeared in the basement membrane of the crypts. Second generation schizonts developed in the lamina propria within these crypt cells whose epithelial origin was confirmed by their interconnection by desmosomes and tight junctions and by their possession of characteristic microvilli. A comparison is made between this invasion of the lamina propria by parasitized cells and invasion of connective tissue by malignant epithelial cells; the possible mechanisms involved are discussed.

Animals↗
PubMed1982

Parasite-host relationships during the development of Eimeria dispersa Tyzzer 1929, in the turkey (Meleagris gallopavo gallopavo) with a description of intestinal intra-epithelial leucocytes.

An electron microscopical study was made on the development of Eimeria dispersa in the small intestine of the domestic turkey. Turkey poults, 10-14 days of age, were inoculated with oocysts and pieces of intestinal tissue were fixed at intervals between 3.5 and 114 h after inoculation. Sporozoites were occasionally seen in enterocytes but more often in 'pale' cells closely resembling lymphocytes. These cells were insinuated between enterocytes and in this study are referred to as intestinal intra-epithelial leucocytes (IEL). Maturation of the first-generation of schizogony occurred in this type of cell. Other generations of schizonts and gametogony occurred in epithelial cells and were characterized by the presence of 'spines' arranged around the parasitophorous vacuole extending into the cytoplasm of the host cell. A limited study of the parasite in the Bobwhite quail, Colinis virginianus, showed that development occurred in similar cells to those of the turkey. The 'spines', which were characteristic of later stages of E. dispersa in the turkey, were also present in this host and seemed to be a characteristic of E. dispersa, not of the host species.

Animals↗
PubMed1982

Mucosal transport of Eimeria tenella in the cecum of the chicken.

A study of the early life history of Eimeria tenella with the electron microscope confirmed that sporozoites do not directly enter the enterocytes of the crypts, in which they develop, but are carried there by host cells. However, these cells are not macrophages, as previously thought, but intraepithelial lymphocytes. The evidence presented demonstrates that sporozoites first penetrate surface enterocytes and then enter intraepithelial lymphocytes that leave the epithelium, pass through the lamina propria and enter the crypts.

Animals↗
PubMed1981

Presence of a complete endothelial barrier between lymph and lymphoid tissue in the lumbar lymph nodes of the duck (Anas platyrhynchos).

The ultrastructure of the lumbar lymph nodes of the domestic duck is described and compared with published accounts of mammalian lymph nodes. The barrier to cell migration between lymphoid tissue and lymph is more formidable in the duck than in the mammal. In the duck the lymphatic endothelium lining the lymph spaces is continuous and bonded with desmosomes whereas in the mammal it is unbonded and fenestrated. In both types of node there are filtering zones and areas of dense lymphatic tissue but their topographical organisation differs. There is no cortex or medulla in the duck lymph node and filtration occurs in extensive lymphatic spaces traversed by numerous trabeculae to which are attached rounded phagocytic macrophages. Dense lymphoid tissue is scattered throughout the node, suspended by trabeculae or attached to the capsule and there are blood vessels analogous to the post capillary venules of mammalian nodes where lymphocytes migrate between blood and lymphoid tissue.

Animals↗
PubMed1977

Morphological distinction between different H serotypes of Escherichia coli.

The structure of the flagellar filaments of 50 Escherichia coli strains, each with a different H antigen, was examined. Although the flagella within each strain were structurally identical, there was variability in flagellar surface pattern between strains with differrent H antigens. Investigation of additional strains confirmed that flagella structure was the same in all strains having the same H antigen. In three pairs of strains with cross-reacting H antigens, the antigenic relatedness was associated with identical flagella structure.

Antigens, Bacterial↗
PubMed1977

Comparison of the flagellins from different flagellar morphotypes of Escherichia coli.

The molecular weights of the flagellins of 13 strains of Escherichia coli, each with a different H antigen, were estimated using polyacrylamide gel electrophoresis. In each case only one major polypeptide was demonstrated, although some strains possessed apparently sheathed flagella. Considerable differences in the molecular weight of flagellin accompanied the previously described structural differences between flagella from strains with different H antigens. The relationship between flagellar diameter and the molecular weight of the corresponding flagellins was similar for both unsheathed and apparently sheathed flagella. Crosss-polymerization occurred between seed consisting of fragment of unsheathed flagella and flagellin solution from apparently sheathed flagella and vice versa. Co-polymerization of flagellin from unsheathed flagella and flagellin from apparently sheathed flagella was also demonstrated. These polymerization experiments indicate that the assembly pattern of flagellin molecules is probably the same in all E. coli flagella. The above and other evidence suggests that there is no true sheath, but that the differences in flagellar surface structure between different E. coli flagella are the result of differences in the superficial parts of the flagellin molecules.

Antigens, Bacterial↗
PubMed1973

Interactions of TRIC agents with macrophages and BHK-21 cells observed by electron microscopy.

TRIC agents do not multiply in mouse peritoneal macrophages in culture but have a toxic effect on them, whereas they multiply readily in BHK-21 cells. Sections of macrophages and of BHK-21 cells fixed during the first 90 min after inoculation were examined by electron microscopy. Macrophages ingested all forms of the organism, which were eventually degraded in lysosomes. However, elementary bodies were distinguished from other TRIC particles by the delay in their transfer to lysosomes. BHK-21 cells ingested elementary bodies selectively, and in these cells the organisms were neither found in lysosomes nor degraded. Instead they showed morphological changes that probably represented an early stage of development.

Acid Phosphatase↗