The salivary glands of Hyalomma anatolicum anatolicum: structural changes during attachment and feeding

The histology and ultrastructure of the salivary glands of male and female H.a. anatolicum ticks have been examined m unfed and feeding ticks with special emphasis on aspects related to the feeding process. The salivary glands of H.a. anatolicum consisted of three types of acinus (acinus I, II and III) in females and an additional type IV acinus in males. The type I acinus was agranular and showed slight morphologic changes during feeding. The presence of cells with ultrastructural features characteristic of epithelia involved in the secretion of hyperosmotic fluids supports the hypothesis that these acini secrete hygroscopic saliva during questing stages to absorb water from an unsaturated atmosphere. There were five granular cell types (a, b, c₁–c₃) in type II acinus, three granular cell types (d, e, and f) in type III acinus, and one granular cell type (g) in type IV acinus. The cells a, d and e secreted most of their granules early in feeding and are considered to be cement precursors. The b and c cells appeared to synthesise and secrete their products throughout feeding and so are likely to secrete anticoagulants, enzymes and other pharmacologically active agents required during feeding. The interstitial cells, which were insignificant in acinar types II, III and IV of unfed ticks, became more distinct during feeding. The type III acinus in females showed remarkable cell transformations, during the course of feeding. The ablumenal interstitial cells of type III acinus, in females formed a basal labyrinth of extraordinary complexity by interdigitating with the basolateral membranes of transformed f cells to form a network of extracellular channels to excrete fluid during feeding. There was an enormous increase in the secretory granules of g cells as the feeding advanced. The secretory granules were released by a process of exocytosis, by direct fusion with the apical membranes and through channels connecting several granules.     

Ultrastructural ontogeny of the labial gland apparatus in termite Prorhinotermes simplex (Isoptera, Rhinotermitidae)

The labial glands in Prorhinotermes simplex consist of secretory cells organized into acini, water sacs and the ducts connecting the gland parts to the basis of the labium. Acini are composed of central and parietal cells. Central cells type I contain predominantly lucent vacuoles and are involved probably in hydroquinone production. They are lacking in soldiers. Type II central cells produce vacuoles of proteinaceous content which are of the same electron density (type IIa) or present in more shades (type IIb). Type IIa cells are present in all older individuals, whereas type IIb are lacking in soldiers and neotenics. Type III cells represent a specific stage of type I cells development, but they are definite functional secretory cells in soldiers. Acini of first instar larvae contain undifferentiated cells which differentiate into type I cells during the second instar. Specific larval central cells start to change into type II cells during first instar. The central cells of presoldiers show a transition from the pseudergate into the soldier situation. The parietal cells keep a uniform structure throughout the whole ontogeny. Only one type of cells form the water sacs in all castes. The cells are very flat with scarce organelles. The water sac cells produce lipid-like secretion, small lucent vacuoles and bunches of angulated vacuoles. The water sac probably functions as water storage organ only. Ontogenetical changes in water sac development are small. The acinar ducts originate inside the acinus where they are formed by flat cells with rare organelles. At the acinus border, cells equipped with mitochondria, microvilli and basal invaginations appear. The water sac ducts are formed by flat cells with rare organelles. Acinar ducts outside the acinus and water sac ducts are equipped with taenidiuam.     

An immunocytochemical marker for the complex granules of tick salivary glands which traces e-granule shedding to interstitial labyrinthine spaces

An antigenic protein (12C), previously isolated from salivary glands of Rhipicephalus appendiculatus, as a possible factor in host resistance to repeated tick infestation, is labeled by protein A-gold immunocytochemistry in adult feeding ticks. It is a component of the gland's complex a-, d- and e-granules and also appears within the chitinous walls of intercalated ducts. In females, between days 4 and 7 of feeding, labeled e-granules appear also within the labyrinthine spaces of acinus type III, apparently released from e-cells as the abluminal interstitial cells initiate formation of a basolateral labyrinth. Granules thus shed are fragmented by interstitial cell processes, some fragments being phagocytized, others disintegrating to single point label scattered throughout the labyrinth. The latter possibly may pass into the acinar lumen. By the eighth day the label is gone from the labyrinth.     

Salivary gland of the tick vector of east coast fever. IV. Cell type selectivity and host cell responses to Theileria parva

Responses of cells in the tick salivary gland to parasitism by Theileria parva were studied by electron microscopy. The gland is composed of three distinct types of acini (I, II, III) which together include ten or more different cell types. Of some 30 infected cells observed in the present study, all were E-cells of acinus III. The parasite thus exhibits a high degree of selectivity for acinus and cell type. The glandular cell invaded undergoes massive hypertrophy and accumulates glycogen deposits in its cytoplasm which may serve as an energy source for the growing intracellular parasite. As synthesis of its secretory material declines the product is packaged in progressively smaller secretory granules. The extensive arrays of endoplasmic reticulum are dismantled and eliminated in autophagic vacuoles. Excess secretory granules are also broken down by crinophagy. After 4 days, sporogony is completed and the host cell contains 30,000–50,000 sporozoites in an electron-lucent cytoplasm largely devoid of cytomembranes and secretory granules. Mitochondria are still present and normal in appearance. The loss of basophilia and secretory granules observed heretofore by light microscopy have been attributed to ingestion and destruction of host organelles by the parasite. The pallid appearance of the cytoplasm has been interpreted as a sign of impending degeneration of the host cell. In electron micrographs no ingestion of organelles by the parasite or degenerative changes were found. The host cell clearly remains viable and metabolically active throughout sporogony. The striking changes in its ultrastructure result from active elimination of organelles and inclusions by the host cell itself in response to parasitism.     

Evidence that developmental changes in type III acini in the tickAmblyomma hebraeum (Acari: Ixodidae) are initiated by a hemolymph-borne factor

During feeding, certain cells in the salivary gland type III acini of the ixodid tickAmblyomma hebraeum Koch undergo major developmental changes. We induced many of these changes in the ablumenal interstitial cells (AbIC), adlumenal interstitial cell (AdIC), and f-cells of type III acini, by transplanting the salivary gland of the unfed female to the hemocoel of a feeding female. In transplants, AbICs enlarged and formed a labyrinth of extracellular spaces. Extensions of AbICs pushed into the AdIC. Autophagic vacuoles were common in AbICs. The f-cells also enlarged and developed autophagic vacuoles. Complex interdigitation occurred between the f-cells and the AbIC. In transplants, the labyrinth was not as extensive as that of fed unoperated females or of operated females. The AdIC, AbIC, and f-cells did not undergo as extensive a development in unoperated fed males as the same cells did in unoperated fed females. In males AbICs did not develop an extensive labyrinth, and the f-cells did not develop beyond a secretory phase. No autophagic vacuoles were observed in any of these cells. When male salivary glands were transplanted into feeding females, AdIC, AbICs and f-cells developed an ultrastructure similar to the same cells in female transplants. Cells from salivary glands of unfed females cultured for 2 days in TC medium 199 resembled the same cells from control unfed salivary glands. The selectivity of these changes supports the conclusion that a hemolymph-borne salivary gland development factor initiated this development.     

Morpho-histochemical characterization of salivary gland cells of males of the tick <Emphasis Type="Italic">Rhipicephalus</Emphasis><Emphasis Type="Italic">sanguineus</Emphasis> (Acari: Ixodidae) at different feeding stages: description of new cell types

This study describes the changes undergone by cells of the salivary glands of unfed and feeding (at day two and four post-attachment) Rhipicephalus sanguineus males, as well as new cell types. In unfed males, types I and II acini are observed with cells “undifferentiated”, undefined 1 and 2 (the latter, with atypical granules), a, c1 and c3; type III is composed of cells d and e; and type IV present cells g. In males at day two post-attachment, type I acini exhibit the same morphology of unfed individuals. An increase in size is observed in types II, III, and IV, as cells are filled with secretion granules. Some granules are still undergoing maturation. In type II acinus, cells a, b and c1–c8 are observed. Cells c7 and c8 are described for the first time. Cells c7 are termed as such due to the addition of polysaccharides in the composition of the secretion granules (in unfed individuals, they are termed undefined 1). Type III acini exhibit cells d and e completely filled with granules, and in type IV, cells g contain granules in several stages of maturation. In males at day four post-attachment, type I acini do not exhibit changes. Granular acini exhibit cells with fewer secretion granules, which are already mature. In type II acini, cells a, b, c1–c5 are present, type III exhibit cells d and e, and type IV contain cells g with little or no secretion. This study shows that in the salivary glands of R. sanguineus males, cells a, c1, and c3 of type II acinus, and cells d and e of type III do not exhibit changes in granular content, remaining continuously active during the entire feeding period. This indicates that during the intervals among feeding stages, gland cells reacquire the same characteristics found in unfed individuals, suggesting that they undergo reprogramming to be active in the next cycle.     

Structural and histochemical changes in the salivary glands of Rhipicephalus appendiculatus during feeding

The salivary glands of the brown ear tick of cattle, R. appendiculatus, from both sexes and at all stages of feeding, were examined as whole glands and as sections for ultrastructural and histochemical changes. The type 1 acinus consists of a basal labyrinth formed by the interdigitations of a central cell and four peripheral cells. These cells form a specialized border with a central constrictor cell which surrounds the acinar duct. The plasma membrane of the central cell is exposed to the duct. The type 1 acini do not appear to secrete active saliva components involved in feeding. The type 2 acini undergo a great increase in synthetic and secretory activity during feeding in both sexes and secrete a lipoprotein probably to form part of the attachment cone and also glycoproteins and esterases of unknown functions. The type 3 acini of both sexes also secrete a lipoprotein probably to form part of the attachment cone. The f cells of these acini in the females transiently secrete a glycoprotein of unknown function and then transform to become part of a water excreting unit. In the males the secretory activity of the granular cells of the type 2 and 3 acini is maintained for further attachments. The type 4 acini of the males accumulate masses of proteinaceous granules. The system of interstitial cells and intercellular spaces in types 2, 3 and 4 acini is large and increasingly active during feeding.     

Ultrastructural changes in the salivary alveoli ofArgas (Persicargas) persicus (Ixodoidea: Argasidae) during and after feeding

Two types of salivary alveoli are present in adultArgas (Persicargas) persicus: agranular type I and granular type II alveoli. Type I alveoli consist of a large central cell surrounded by a constrictor cell and peripheral cells with numerous infoldings of the basal membrane similar to epithelia involved in active transport. The basal infoldings form a previously undescribed successively convoluted membranous pattern which may increase the capability of peripheral cells for active transport. Type II alveoli consist of three granular cells (a, b, c) and two agranular (adlumenal and ablumenal interstitial) cells. Golgi bodies and rough endoplasmic reticulum are probably involved in the granule formation. The granules are discharged within 5–10 min after feeding commences, and presumably contain anticoagulant substances and pharmacologically active agents that promote the blood flow of the host during tick feeding. Although the adlumenal cells are not structurally affected by feeding, ablumenal cells develop into transporting epithelia.     

Salivary gland ultrastructure of the unfed adult and feeding female of Haemaphysalis (Rhipistoma) leachi (Ixodoidea: Ixodidae)

The paired salivary glands of unfed adult Haemaphysalis (Rhipistoma) leachi contain one type of agranular and three types of granular alveoli connected to a salivary duct system. Type I agranular alveoli consist of one large, central cell surrounded by peripheral cells with numerous basal membrane infoldings indicative of epithelia involved in fluid transport. Glycogen particles, lipid-like droplets, and the parallel pattern of infolded membranes disappeared from the peripheral cells during feeding. Types II, III, and IV granular alveoli contain some agranular interstitial epithelial cells, cap cells, and fundus cells, but are predominantly composed of structurally different granular cell types a, b, c, d, e, and f. Agranular cells develop during the early stages of feeding. Granular a, c, e, and f cells release their granules directly after attachment to the host and possibly are involved in cement secretion required for firm attachment to it. The b cell granules are replaced by b₁ filamentous granules during feeding. Golgi bodies and rough endoplasmic reticulum (RER) participate in the formation of most types of granules. The d cells contain lamella-like structures and condensing vacuoles, probably responsible for lysosome formation. The main salivary duct and all types of alveoli are innervated by neurosecretory axons.     

Secretory process of salivary glands of female Amblyomma cajennense (Acari: Ixodidae) ticks fed on resistant rabbits

Ticks have great economic and health importance since infested animals have reduced milk and meat production, and, besides that, they are expensive ectoparasites to control. While feeding, ticks can transmit to their hosts a large amount of pathogens, including Rickettsia rickettsii responsible for the ??spotted fever?? or ??fever of the mountains.?? It is known that animals infested with ticks or artificially immunized with their salivary gland extracts develop resistance, which is related to a decrease in engorged female weight, in egg-laying by adults, in egg viability and, in some cases, in the capacity of pathogens transmission. The present study aimed to examine morpho-histochemically the female salivary glands of semi and engorged Amblyomma cajennense fed on resistant rabbits. The results revealed that acinus I had no changes when compared to that of females fed on naive rabbits. The c cells of acinus II showed signs of early degeneration, which may result in feeding efficiency decrease. In acinus III d cells, activity time was longer. Such occurrence was associated with the time of female fixation, which increased in females fed on resistant hosts.     

Transient Swelling of Salivary Acinus Induced by Acetylcholine Stimulation: Water Secretion Pathway in Rat Submandibular Gland

The volume changes of isolated acini and acinar cells from rat submandibular glands were measured from digitized images recorded upon stimulation of acetylcholine (ACh) or reduction of the perfusate osmolarity and water secretion pathway in salivary gland was studied. When acinus is exposed to a hyposmotic solution, water flows into the acinar cells and into the lumen via acinar epithelia. If the water enters the lumen chiefly via the cells, the swelling of the lumen would follow the same time course as the cell swelling or slower. The results show that reduction of the perfusate osmolarity evoked a transient increase followed by a gradual increase in the volume of unstimulated acinus, while it evoked only a gradual increase in the volumes of unstimulated acinar cells. Thus, the time course of the acinar swelling is faster than that of the acinar cell swelling. Reduction of the perfusate osmolarity also evoked a transient swelling in ACh stimulated acini. When acinus is stimulated by ACh, water also flows into the lumen via acinar epithelia according to the osmotic gradient which was generated by the active electrolyte transport of acinar cells. If the water enters the lumen chiefly from the cells, there would be no overall change in acinar volume. The results show that stimulation of ACh (5 μm) evoked a transient increase followed by a gradual decrease in the volume of the acinus, while it evoked only a decrease in the volume of acinar cells. Video-enhanced optical microscopy exhibited that ACh stimulation caused transient swelling of the luminal space, prior to causing the volume of acinar cells to decrease and the transient swelling of the lumen followed the same time course as that of acinus. Thus, the transient acinar swelling is explained by the transient swelling of luminar volume. These results suggest that water is probably drawn into the lumen from interstitial space directly in the salivary acinus. Received: 3 February 1997/Revised: 29 October 1997     

Ultrastructure of salivary glands of Ornithodoros (Ornithodoros) moubata (Ixodoidea: Argasidae)

The paired salivary glands of unfed adult Ornithodoros (Ornithodoros) moubata are composed of type I (agranular) and type II (granular) alveoli. Type I alveoli consis of one large central cell surrounded by peripheral cells having the morphology of fluid-transporting epithelia. Type II alveoli contain granular and agranular cells; the former are comprised of morphologically distinct types of cells (a, b, and c) containing granules of different structures and chemical composition with respect to polysaccharide and protein. The agranular cells are the interstitial and cap cells. Golgi bodies and rough endoplasmic reticulum (RER) are found in all granular cells and apparently are involved in granule formation. No appreciable structural changes were observed in type I alveoli during or after feeding. Type c cell granules are released before granules from types a and b cells and may contain anticoagulant substances that promote the blood flow of the host during the tick feeding. Although the cap cells are not structurally affected by feeding, interstitial cells are developed into transporting epithelia.     

Morphological changes in the salivary glands of Amblyomma cajennense females (Acari: Ixodidae) in different feeding stages on rabbits at first infestation

This study examined salivary glands of unfed, partially engorged, and engorged females of the tick Amblyomma cajennense on rabbits at first infestation using histological and histochemical techniques. In type I acini, no significant changes were observed among the three feeding conditions. In type II acini of unfed females, c1, c2, and c4 cells were described for the first time in this species. In a comparison among the three feeding conditions, an increase in this acinus was observed, due to the increase in secretion in c1, c2, and c4 cells and the appearance of c3 cells. In engorged females, some cells were still active. Type III acini presented cells d, e, and f containing secretion in unfed females. In partially engorged females, these cells were devoid of secretion. In engorged females, type III acini exhibited a reduced lumen. After engorgement, all acini underwent a degenerative process, as observed in females after two to five days post-engorgement.     

Development of the labial gland of the ponerine ant Pachycondyla obscuricornis (Hymenoptera, Formicidae) during the pupal stage

The labial gland of adult workers of the ant Pachycondyla obscuricornis is made up of many acini, each consisting of one central cell surrounded by approximately 10 parietal cells. Both cell types are associated with a system of ramified canaliculi that remove the secretion towards a ductule outside the acinus. These ductules, each associated with one acinus, fuse together and form a ramified system of ducts, ending in two paired ducts. These paired ducts widen to form a reservoir and anteriorly join into a common unpaired duct, which ends at the base of the labium. During development in the pupal stage, epithelial acini are formed first, consisting of a monolayered epithelium lining a central lumen. In these acini, one cell grows out to become the central cell, while the others will re-arrange around it to form the parietal cells. At the end of the pupal stage, the canaliculi are formed inside the acini by the central and parietal cells that secrete a lipidic substance and a cuticle. This gland type, which also occurs in some other Hymenoptera, is structurally different from the epithelial glands and the glands consisting of bicellular units, that have been traditionally distinguished until now.     

Rhipicephalus (Boophilus) microplus (Canestrini, 1887) (Acari: Ixodidae): acid phosphatase and ATPase activities localization in salivary glands of females during the feeding period

This study investigates the presence and the localization of acid phosphatase and ATPase in the salivary glands of Rhipicephalus (Boophilus) microplus female ticks during feeding. Semi-engorged females showed a larger amount of acid phosphatase compared to those at beginning of feeding, localized mainly in the apical portion of the secretory cells, and in the basal labyrinth of the interstitial cells. Ultrastructural observations also demonstrated its presence in secretion granules and inside some nuclei of secretory cells at beginning of feeding. Acid phosphatase in a free form probably has a hemolymph and/or ribosomal origin and participates in salivary gland secretion control. ATPase was detected in basal membrane of all types of acini and/or in the cytoplasm of the secretory cells at both feeding stages. The enzyme activities found strongly suggests that cell death by apoptosis occurs during the degenerative process.     

Salivary gland of the tick vector (R. appendiculatus) of East Coast fever. I. Ultrastructure of the type III acinus

The brown ear tick Rhiplcephalus appendiculatus is the vector for East Coast fever, a disease that seriously limits livestock production in East Africa. The sporozoites of the infectious agent Theileria parva develop in the tick salivary gland. This paper describes the organization of the type III acinus of the gland and establishes unambiguous ultrastructural criteria for identification of the three secretory cell types: the d-cell, e-cell and f-cell. These observations are basic to exploration of possible cell-type specificity of the invading theileria and other aspects of host-parasite relations.     

Functional recovery of fluid drainage precedes lymphangiogenesis in acute murine foreleg lymphedema

Secondary lymphedema in humans is a common consequence of axillary lymph node dissection (ALND) to treat breast cancer. It is commonly hypothesized that lymphatic growth is required to increase fluid drainage and ameliorate lymphedema. Although there is a pronounced alteration in the balance of interstitial forces regulating fluid transport that sustains the chronic form of lymphedema, it is presently unknown whether changes occur to the balance of interstitial forces during acute lymphedema that may play a role in the recovery of fluid drainage. Here, we compared the relative importance of lymphangiogenesis of lymphatic vessels and interstitial flows for restoring fluid drainage and resolving acute lymphedema in the mouse foreleg after ALND. We found that removal of the axillary lymph nodes reduced lymph drainage in the foreleg at days 0 and 5 postsurgery, with fluid tracer spreading interstitially through subcutaneous tissues. Interstitial fluid drainage returned to normal by day 10, whereas functional regrowth of lymphatic vessels was first detected by indocyanine green fluorescence lymphography at day 15, demonstrating that the recovery of interstitial fluid drainage preceded the regrowth of lymphatic vessels. This was confirmed by the administration of VEGF receptor-3-neutralizing antibodies, which completely blocks lymphatic regrowth. It was found that the recovery of interstitial fluid drainage and the natural resolution of acute lymphedema produced by ALND were not hindered by VEGF receptor-3 neutralization, demonstrating that interstitial fluid drainage recovery and the resolution of acute lymphedema are lymphangiogenesis independent. The data highlight the central role of the interstitial environment in adapting to lymphatic injury to increase fluid drainage.     

Morphology of the exocrine glands of the frog skin

Frog skin contains three distinct types of exocrine glands: granular (poison), mucous, and seromucous. The granular gland forms a syncytial secretory compartment within the acinus, which is surrounded by smooth muscle cells. The mucous and seromucous glands are easily identifiable as distinct glands. The serous and mucous secretory cells are arranged in a semilunar configuration opposite the ductal end and are filled with granules. Within the acinus, located at the ductal pole of the gland, are distinct groups of cells with few or no granules in the cytoplasm. In both the mucous and seromucous gland there is a cell type with abundant mitochondria; the one in the mucous gland is located in the region adjacent to the secretory cells. The duct of these glands is two-layered, with the individual cells appearing morphologically similar to the layers of the skin epithelium as the duct traverses the skin. The duct appears to be patent throughout its length. The morphological heterogeneity and distinct distribution of the cell types within the gland acinus may be indicative of a functional heterogeneity that allows the production of distinctly different types of secretion from the same gland type, depending on the type of stimulus.     

Lowering of interstitial fluid pressure in rat submandibular gland: a novel mechanism in saliva secretion

The submandibular gland transports fluid at a high rate through the interstitial space during salivation, but the exact level of all forces governing transcapillary fluid transport has not been established. In this study, our aim was to measure the relation between interstitial fluid volume (V(i)) and interstitial fluid pressure (P(if)) in salivary glands during active secretion and after systemically induced passive changes in gland hydration. We tested whether interstitial fluid could be isolated by tissue centrifugation to enable measurement of interstitial fluid colloid osmotic pressure. During control conditions, V(i) averaged 0.23 ml/g wet wt (SD 0.014), with a corresponding mean P(if) measured with micropipettes of 3.0 mmHg (SD 1.3). After induction of secretion by pilocarpine, P(if) dropped by 3.8 mmHg (SD 1.5) whereas V(i) was unchanged. During dehydration and overhydration of up to 20% increase of V(i) above control, a linear relation was found between volume and pressure, resulting in a compliance (DeltaV(i)/DeltaP(if)) of 0.012 ml.g wet wt(-1).mmHg(-1). Interstitial fluid was isolated, and interstitial fluid colloid osmotic pressure averaged 10.4 mmHg (SD 1.2), which is 64% of the corresponding level in plasma. We conclude that P(if) drops during secretion and, thereby, increases the net transcapillary pressure gradient, a condition that favors fluid filtration and increases the amount of fluid available for secretion. The reduction in P(if) is most likely induced by contraction of myoepithelial cells and suggests an active and new role for these cells in salivary secretion. The relatively low interstitial compliance of the organ will enhance the effect of the myoepithelial cells on P(if) during reduced V(i).