Laboratory indicators of the bone turnover In the process of bone remodelling, the cross-link fragments of collagen enter the blood and then may be detected in the serum or urine.

Lactoferrin  Protein that contains iron, found in milk and in secondary granules of neutrophils in which it is involved in antimicrobial pathways by absorbing iron from the environment. Iron is crucial for the growth and reproduction of microorganisms.

LAK cells  These are lymphokine (mainly IL-2)-activated killer cells. NK cells are most frequently subject to activation, less frequently cytotoxic T lymphocytes. LAK cells are also able to lyse those target cells that cannot be lysed by less active NK cells. This has recently led to their use in the treatment of certain tumours.

Lambert–Eaton syndrome A complication of intrathoracic tumours, especially small cell lung cancer, though it may also be idiopathic, especially in younger women. Muscle weakness is the primary manifestation, but myalgias and paraesthesiae can occur.

Aetiology – decreased release of acetylcholine in the nerve terminals

Laminin Glycoprotein of high molecular weight (MW 900 kDa) comprising three (alpha, beta and gamma) polypeptide chains. Fifteen different forms of laminin have been identified. Laminin belongs to adhesive molecules and is part of the intercellular matrix, where it is bound to collagen type IV, heparan and glycosaminoglycans participating in the formation of the basement membrane of many tissues, including vessels. It is involved in the adhesion and chemotaxis of neutrophils. Laminin is the morphogenic factor of epithelial cells and hepatocytes, and by binding to receptors on the surface of nerve cells, it enables mutual aggregation of these cells and the production of dendrites. It is produced by macrophages. The importance of laminins is illustrated by the fact that the dysfunctional structure of laminin-2 is the cause of some types of muscular dystrophy.

Large granular lymphocytes – see LGL (large granular lymphocytes)

Lazy leucocyte syndrome An older term for unidentified conditions associated with deficient chemotaxis of leucocytes leading to increased risk of pyogenic infections. Nowadays, specific causes of deficient chemotaxis have been identified, so the nomenclature has been modified, e.g. leucocyte adhesion deficiency (LAD) syndrome.

LcSSc – see Systemic sclerosis (SSc).

LE cells The history of antinuclear antibodies (ANA) began in 1948 when Hargreaves described the phenomenon of LE cells. An LE cell is a polymorphonuclear (PMN) leucocyte, which has phagocytosed the released nuclear material of another leucocyte. Antibodies against nucleosomes, which in vitro bind to a released nucleus, are responsible for the LE phenomenon. As a consequence of the binding, complement is activated, with opsonisation of nuclear material, and finally phagocytosis by a PMN leucocyte occurs. This results in the formation of a large lucid phagocytosed nucleus surrounded by small amounts of cytoplasm. The original nucleus of a phagocytosing leucocyte is compressed to the cell membrane. LE cells are typical for systemic lupus erythematosus, although they may occasionally be present in rheumatoid arthritis and systemic sclerosis. At present the detection of LE cells has been superseded and more sensitive techniques, such as immunofluorescent ANA detection, are used.

Lectins Proteins and glycoproteins which are able to specifically recognise and bind to different mono-, di- and trisaccharides. They activate the agglutination of erythrocytes and other cells and are polyclonal (non-specific) mitogens of lymphocytes (e.g. phytohaemagglutinin, concanavalin A). This property is enabled by the presence of glycocalyx, which is located on the surface of most of the cells and which contains different oligosaccharide chains. Lectins were originally isolated from plants but now are also known to be present in animals (so-called collectins in human and other mammals) and microorganisms.

Ledderhose’s disease A plantar fascial fibromatosis, also known as Morbus Ledderhose, and plantar fibromatosis, is a relatively rare non-malignant thickening of the plantar aponeurosis. It may occur at any age with the greatest prevalence at middle age and beyond. This disorder is more common in men than women, and it is often associated with Dupuytren’s disease.

Leflunomide A dihydroorotate dehydrogenase inhibitor which selectively blocks de novo synthesis of pyrimidines in rapidly proliferating activated lymphocytes. This suspends activated autoimmune lymphocytes in the G1/S phase of cell cycle, whilst not affecting other lymphocytes in G0 phase, as long as they are not needed in the immune response. Though primarily acting as an immunomodulating agent with anti-inflammatory activity, leflunomide does not have the property of a non-selective immunosuppressant. It inhibits IL-2 synthesis and the expression of adhesive molecules, decreasing the number of neutrophils that infiltrate the joint cavity.