The influence of dietary fat on the interaction of lymphocytes with high endothelial venules.

The specific adherence of lymphocytes to high endothelial venules (HEV) represents the first step in the lymphocyte emigration from blood into most lymphoid tissues. The interaction of lymphocytes with HEV exhibits a remarkable organ specificity, which appears to be mediated by complementary receptors on both recirculating lymphocytes (homing receptors) and tissue-specific HEV (vascular addressins). The expression of homing receptors varies and depends on factors such as lymphocyte subtype, stage of activation and maturation. As these receptors are glycoproteins, which are anchored in the cell membrane, it can be envisaged that their position and function are determined by the overall composition of the cell membrane itself. In this study we investigated the significance of dietary fat concentration and saturation for the interaction between lymphocytes and HEV. In addition to these functional studies, the expression of homing receptors in combination with T and B cell markers were analyzed. Using immunohistochemistry the effect on the presence and characteristics of lymphocytes and HEV in situ was studied. Changes in the dietary fatty acid composition resulted in an altered ability of T and B cells to adhere to HEV, without affecting their binding preference. The changed adhesion patterns seemed to be associated with alterations in the expression of adhesion molecules, that are essential for the lymphocyte migration. The latter observation might in turn be explained by the observed modifications in the fatty acid composition of the lymphocytes. These results suggest a role for the fatty acid composition of the nutrition in the process of lymphocyte recirculation.

The fatty acid composition of the lymphocyte cell membrane. Influence on interactions with high endothelium and the expression of homing receptors.

By incubating mouse lymphocytes in vitro with various fatty acids in an otherwise lipid-free medium, the lipid composition of the cell membrane was varied. These changes resulted in an altered adhesion pattern on High Endothelial Venules (HEV) using an in vitro adherence assay. Incubation with linoleic acid (18:2) resulted in an increased adherence of T and B lymphocytes, linolenic acid (18:3) had no influence and both arachidonic acid (20:4) and arachidic acid (20:0) resulted in a decreased adherence of the two cell types when the adherence assay was performed using HEV from peripheral lymph nodes. Using HEV from mucosa associated Peyer's patches, T and B cells incubated with arachidic acid or arachidonic acid were less able to adhere this type of HEV. After incubation with linoleic acid, T lymphocytes adhere better to the Peyer's patches HEV whereas B cells showed a decrease in adherence and linolenic acid resulted in a decreased adherence of only B lymphocytes. FACS analysis revealed that MEL-14 expression as well as the expression of LFA-1 was somewhat elevated in intensity on T and B lymphocytes after incubation with linoleic acid. In contrast, the intensity for MEL-14 had decreased after arachidic acid or arachidonic acid. In case of arachidic acid the LFA-1 expression had also decreased. No changes were found after incubation with linolenic acid. The results suggest a role for the lipid composition of the membrane in recirculation patterns of lymphocytes.

The functional activity of high endothelial venules: a role for the subcapsular sinus macrophages in the lymph node.

Adherence of lymphocytes to high endothelial venules (HEV3) is the first step in normal lymphocyte emigration and recirculation. At sites of chronic inflammation, venules often become high-walled and may also be a site for leukocytes to leave the bloodstream. The immunologic and inflammatory mediators, responsible for these effects on endothelial cells, may be important for the maintenance and function of HEV in physiological conditions. It is reported here that the morphological and functional aspects of HEV can be studied by organ cultures of lymph nodes (LN). At 24 h of culture, the appearance of the node was still quite normal, whereas the HEV became flat-walled, with a 45-50% reduction in the capacity to bind lymphocytes. This decrease in function of HEV could be reduced when LN were cultured in the presence of lipopolysaccharides (LPS). The effect of LPS on the function of HEV was presumably mediated by macrophages in the subcapsular sinus, because HEV in LN, which were depleted of subcapsular sinus and medullary macrophages previous to culture, could not be stimulated by addition of LPS to the cultures.

The effects of bacterial lipopolysaccharide (LPS) on high endothelial venules and interdigitating cells in mouse lymph nodes.

Migration of lymphocytes into lymph nodes is directly controlled by interaction of lymphocytes with the high endothelial venules (HEV), located in T cell-dependent areas of lymph nodes. Little is known about the mechanisms that regulate the activity of the HEV and the specificity of interaction with lymphocytes in various lymphoid organs. It has been suggested that the non-lymphoid interdigitating cells (IDC) play a role in maintaining the integrity of T cell areas. We therefore wished to determine whether the function of the HEV could be influenced by disturbing the integrity of the T cell area. This was assayed in mice by injecting bacterial lipopolysaccharide (LPS) in the hind footpad. The T cell-dependent areas of mouse popliteal lymph node were studied using immunohistochemistry, and attention was paid to the HEV specificity using short-term in vivo localization assays and in vitro lymphocyte binding assays. After LPS administration, apparent changes in the number of interdigitating cells and T cells in the draining lymph node were found. In addition, interdigitating cells lost their typical dendritic appearance. However, after LPS treatment, neither size, localization nor receptor specificity for lymphocyte subsets of HEV differed from control HEV. Although administered subcutaneously in the footpad, the effect of LPS on T cells and IDC was much more dramatic in the spleen than in the draining lymph nodes. This points to a difference in the processing of the endotoxin in the two organs.