RETICULAR FABRIC (textus connectivus reticularis (LNH); lat. reticulum grid; synonym mesh fabric) — a kind of the connecting fabric consisting of the reticular macrophages and reticular fibers concluded in the main intercellular substance and forming the friable three-dimensional network which is a basis of the hemopoietic and lymphoid bodies.
Ideas of R. of t. radiobiologies, immunology, transplantology formed within many decades, but only in the last 10 — 15 years, thanks to achievements of cytogenetics, essentially new data on its differentiation, structure and function were obtained.
In R.'s embryogenesis of t. it is differentiated from mesenchymas (see) and in the early post-natal period gradually gets a structure of mature fabric.
Reticular macrophages (cellulae reticulares) carry to cells of fibroblastichesky type, along with the fibroblasts, chondroblasts and osteoblasts combined under the name «mekhanotsita». Reticular macrophages (fig. 1) have the flattened, spindle-shaped or star-shaped form with a smooth surface; a kernel — angular or extended. Extent of development of organellas, in particular a granular cytoplasmic reticulum and Golgi's complex (see. Golgi complex ), it is variable and depends on a functional condition of a reticular macrophage. The next reticular macrophages or shoots of the same cells contact with each other by means of connections of type intermediate or desmosomes (see).
In view of the fact that it is often difficult to distinguish reticular macrophages among the mass of the hemopoietic cells, their identification is possible only during the use submicroscopy (see), histochemical methods of a research (see) and methods of an immunohistochemistry (see. Immunomorphology ) or combinations of these methods allowing to reveal with high degree of reliance reticular macrophages, and also to identify them from cells, externally similar to them systems of mononuclear phagocytes (see).
Histochemical properties of reticular macrophages are defined by organ, and also specific features. The person has reticular macrophages of a white pulp spleens (see) differ from macrophages (see) lower activity esterases (see) and acid phosphatases (see), and from interdigitiruyushchy cells (a kind of mononuclear phagocytes) — lack of activity of ATP-ase. In reticular macrophages of a lymphocytic crown limf, follicles of a spleen clear activity 5 '-nucleotidases (tab.) comes to light.
Activity 5' - nucleotidases is defined also in reticular macrophages of a white pulp of a spleen of rats and Guinea pigs, but is absent at rabbits. Reticular macrophages of marrow of mice and rats are characterized by activity of the alkaline phosphatase which is localized on their plasma membrane. They differ in this sign from macrophages, in to-rykh activity of the acid phosphatase which is localized in comes to light lysosomes (see). Such morfol. type of reticular macrophages often call fibroblastichesky.
In the light (germinative) centers limf, follicles of a spleen and lymph nodes (see) the special type of reticular macrophages — dendritic reticular macrophages is described. They are distinguished by the large sizes, a kernel of irregular shape with the expressed kernel, numerous smooth bubbles in cytoplasm. A characteristic sign of dendritic reticular macrophages are the long branching shoots with numerous folds which are deeply getting between surrounding lymphoid cells (fig. 2). Shoots of dendritic reticular macrophages together with cytoplasmatic protrusions of immunoblasts (V-lymphocytes) create complex network in the form of a labyrinth. In intercellular space among shoots microvesicular structures and globular dense particles with a diameter of 20 — 70 nanometers are localized. In the field of contact of shoots of dendritic reticular macrophages structures of type are visible desmosomes (see). Unlike macrophages with the painted inclusions and other mononuclear phagocytes dendritic reticular macrophages have lower activity of esterase and acid phosphatase, but high activity 5 '-nucleotidases. On a number of histochemical signs they can be similar to mononuclear phagocytes: macrophages of a red pulp of a spleen, metallophilic (argyrophil) cells of the fringe region limf, follicles, macrophages with the painted inclusions. Criterion for identification of dendritic reticular macrophages ability of these cells to connect (but not to englobe) cell-bound immune complexes on the surface is decisive.
Reticular fibers (fibrae reticulares) which are R.'s part of t., consist of the fibrilla of various diameter concluded in homogeneous, dense main intercellular substance. Fibrilla with a diameter of 20 — 50 nanometers has the axial striation characteristic of mature collagen. Thin fibrilla with a diameter of 10 nanometers is localized on the periphery of reticular fibers. Reticular fibers are always shrouded in cytoplasm of reticular macrophages in the form of a cover (are invaginated in a cytolemma), the gleam to-rogo is always reported with intercellular space. In lymphoid bodies the network of reticular fibers is developed stronger, than in marrow, and in a thymus gland - dependent zones limf, nodes it more friable, than in cortical and marrow.
According to biochemical and immunochemical analyses, reticular fibers consist of collagen III of type (see. Collagen ) and not collagenic component in the form of amorphous interfibrillar substance with the expressed immunogene properties. As a part of not collagenic component proteins (90%), carbohydrates (4%) and lipids (4%) are identified. For identification of reticular fibers widely use various options of impregnation by silver. Immunohistochemical and immunofluorescent methods of identification of reticular fibers begin to enter daily practice (see. Immunomorphology , Immunofluorescence ), to-rykh use of specific antiserums to collagen of different types is the cornerstone.
River of t. forms a stroma and is the carrier of specific organ functions of marrow and peripheral lymphoid bodies (spleens, limf, nodes, solitary and group limf, follicles went. - kish. path). After it was experimentally proved that reticular macrophages of a gistogeneticheska are independent from hemopoietic, their began to refer to category of the stromal elements responsible for creation of the specific microenvironment providing migration, sorting, replication and a differentiation of the hemopoietic and lymphoid cells. Reticular macrophages are capable to recover an initial microenvironment at damage of the bodies containing R. of t., or to transfer it at ectopic transplantation. In all cases at first the reticular stroma is recovered, and then she repopulirutsya (becomes populated) by the hemopoietic or lymphoid cells (see. Adenoid tissue ). In marrow reticular macrophages create also adventitious layer of sinusoidny capillaries and in the conditions of a normal hemopoiesis cover up to 60% of their surface. The long branching shoots of reticular macrophages enter specific interaction with the hemopoietic cells granulotsitarno-go a number of a differentiation (see. Hemopoietic bodies ). Concentration of reticular macrophages is increased near an endosteum.
Experimental data confirm preservation in post-natal ontogenesis of gistogeneti-chesky proximity between different types of mekhanotsit (fibroblasts, cartilaginous, bone, reticular macrophages). So, at cultivation of marrow of in vitro there are colonies clones of fibroblasts; nek-ry at the return transplantation in an organism create marrowy body (the site of the bone tissue surrounding the marrow) occupied by the hemopoietic cells of these colonies. These data show that among reticular macrophages of marrow there are elements capable to be transformed to true fibroblasts (judging by their ability to synthesize collagen I and III of types), and at the same time, the showing osteogene properties. In other pilot model the marrowy body results from consecutive morphogenetic processes under the influence of the inductor — the demineralized bone matrix implanted into hypodermic connecting fabric. According to Reddi, Gay, Gay, Miller (And. N. Beddi, V. Gay, S. Gay. E. J. Miller, 1977), in this case under the influence of the inductor occurs consecutive transformation of fibroblasts in cartilaginous, bone, and then reticular (stromal) macrophages. Apparently, reticular macrophages of marrow are also capable to be transformed to the lipoblasts participating in creation of hemopoietic microenvironment (in red marrow). Normal reticular macrophages are distinguished by high radiation resistance, and they practically do not share.
There is an opinion that on a surface of dendritic reticular macrophages there are membrane receptors for immunoglobulins (see), with to-rymi cell-bound immune complexes of antigens contact antibodies. According to other opinion, antigens (see) are just slowly filtered through the labyrinth created by shoots of dendritic reticular macrophages. Binding of antigen happens quicker at previously immunizirovanny animals (in 0,5 — 2 hours), than at neimmunizirovanny (in 4 — 24 hours). In parallel also the ultrastructure of dendritic reticular macrophages changes. In experiences on rabbits it is shown that in the course of formation of the light centers dendritic reticular macrophages are transformed from fibroblastichesky reticular macrophages of an adjacent lymphocytic crown. At the same time reticular macrophages lose activity of an alkaline phosphatase (and, apparently, ability to a voloknoobrazovaniye).
With age in R. of t. the number of fibrous structures increases. Irreversible substitution of a reticular stroma fatty tissue and the termination of a hemopoiesis is characteristic of marrow. With age and pathological changes of R. of t. dysfunction of the hemopoietic and lymphoid bodies is closely connected. At impact of high ionizing radiation doses on R.'s organism of t. does not regenerate, and it is replaced with fibrous. The myelofibrosis is characterized by intensive proliferation of fibrogenny cells and the subsequent massive adjournment of collagen I, III and IV of types. Participation of reticular macrophages in synthesis of fibrous proteins of amyloid is shown (see. Amyloidosis ). The defeat of actually reticular stroma which is followed by disturbance of a hemopoiesis can not always be revealed morphologically. Therefore the important part is assigned to methods of cloning of stromal cells in vitro, studying of their interaction with the hemopoietic and lymphoid cells in liquid and agar cultures.
See also Connecting fabric .
&Tablitsa.Nbsp; The COMPARATIVE CHARACTERISTIC of ACTIVITY of ENZYMES IN RETICULAR MACROPHAGES AND MONONUCLEAR PHAGOCYTES (MACROPHAGES) BÉLA PULPY SELEZENKI CHELOVEKA according to Müller-Hermelinka (H. To. Muller-Hermelink), etc. (1974)
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H. G. Hrushchov, V. I. Starostin.