What is pyloric caeca

In some cases, these IELs were small round cells similar to other IELs previously described in rainbow trout [5] , whereas some other cells contained pseudopodia and a morphology that may suggest an antigen presenting role. The figures show a magnification image and an insert figure of the general location in which the detail was observed. Having established the presence of tissue B cells all along the digestive tract, we proceeded to study their response to an oral vaccination protocol that had previously proved effective in controlling viral replication [16].

As a first step, we studied the levels of transcription of the IPNV VP2 gene along the different segments of the digestive tract at day 10 post-vaccination, when the VP2 levels were maximal in the pyloric caeca segment data not shown. The highest levels of VP2 transcription were observed in the first segments, the esophagus, stomach and pyloric caeca Fig.

Although still detected, the transcription of VP2 was much lower in the midgut and hindgut segments. These results reveal that the DNA vaccine is effectively taken up and transcribed by enterocytes all along the digestive tract. Open circles represent relative transcription levels from individual fish, whereas black squares represent mean values in each segment.

To analyze the differences in B cell response to oral vaccination among the gut segments, we first studied the transcription levels of different Ig genes in vaccinated and control animals mock-vaccinated either with the empty plasmid or with the alginate microparticles alone. IgM, IgT and IgD transcription levels were observed all along the digestive tract in all experimental groups. However, only in the pyloric caeca region, IgM transcription was significantly higher in vaccinated fish than in control groups either injected with the empty plasmid or with the alginate alone Fig.

In the case of IgT and IgD transcription, again, only in the pyloric caeca region the values obtained in the vaccinated group were significantly higher than those obtained in the control groups Fig. Finally, a third group received the same volume of an empty microsphere suspension. At day 10 post-vaccination, trout were sacrificed and the different segments of the digestive tract removed for RNA extraction and analysis of immune gene transcription through real time PCR. For IgM, specific primers have been previously designed to distinguish between the membrane form and the secreted form of IgM [25].

Using these primers, we observed that, for both the secreted and the membrane form of IgM, transcription levels were always lower in the two more distal segments, the midgut and the hindgut Fig. In the pyloric caeca region, although we observed a higher transcription of the secreted form of IgM in vaccinated animals, the differences were not significantly different than those observed in the group mock-vaccinated with the empty alginate microspheres Fig.

Surprisingly, these values were significant in comparison to the levels detected in the group vaccinated with the empty plasmid, as there was a marked down-regulation of the transcription levels in this group.

The reason for this down-regulation in the levels of transcription of secreted IgM observed in response to the empty plasmid is unknown and should be further investigated.

Concerning the levels of transcription of the membrane form of IgM, we found levels of transcription significantly higher in the pyloric region of the vaccinated fish in comparison to those obtained in the control fish Fig. Trout were orally vaccinated and sampled as described in the legend of Figure 4 and levels of secreted IgM A and membrane IgM B transcription in the different segments were studied through real time PCR.

Pax5 is a B cell-specific transcription factor down-regulated through the maturation of B cells due to the induction of the transcriptional repressor Blimp1 [26]. Blimp1 transcription remained almost undetected in the esophagus and the stomach Fig. Then the levels increased in the pyloric caeca region, to decrease again in the last two segments.

In response to vaccination, it was only in the pyloric region, where differences between the vaccinated group and the control groups were significant. This same response in the pyloric caeca region was observed for Pax5 transcription Fig.

Trout were orally vaccinated and sampled as described in the legend of Figure 4 and levels of Blimp1 A and Pax5 B transcription in the different segments were studied through real time PCR. To understand whether the variations in the levels of transcription of the different immune genes analyzed were directly produced in response to vaccine transcription, we conducted a Pearson correlation analysis using the data from vaccinated animals.

Unexpectedly, there was no correlation of VP2 transcription and IgD transcription in this segment; whereas there was a correlation between this two sets of data in the esophagus, the stomach and the hindgut segments. These data further confirm that the up-regulation in the levels of transcription of Ig variants and transcription factors observed in the pyloric caeca are directly produced by the oral vaccination procedure.

Trout were orally vaccinated as described in the legend of Figure 4 and sampled at day 10 post-vaccination. The quantification was performed in triplicate in 3 individual fish per group.

Given that both Blimp1 and Pax5 transcription levels were up-regulated in response to oral vaccination in the pyloric caeca, despite being a priori negatively correlated, we decided to further investigate the transcription of these factors. As already observed in the vaccination trial, Blimp1 was not significantly transcribed in the foregut and stomach; however, mRNA levels were detected in the pyloric caeca, midgut and hindgut segments, at levels significantly higher than those observed in PBLs Fig.

On the other hand, Pax5 was only faintly detected in the esophagus, pyloric caeca and hindgut, whereas the levels of Pax5 transcription in PBLs were times higher Fig. These results, together with the fact that only Blimp1 and not Pax5 levels were correlated to VP2 transcription in the pyloric caeca, suggest that B cells that respond to vaccination in the pyloric caeca have a Blimp1 high Pax5 low phenotype.

Constitutive levels of Blimp1 A and Pax5 B transcription in different segments of the trout digestive tract after perfusion were compared to transcription levels observed in PBLs. An important vascularization and endothelial cells were also observed in these adipose structures. To verify whether these immune cells embedded in the adipose tissue also responded to stimulation, we analyzed the levels of transcription of IgM and IgT in this accumulation of adipose tissue associated to the digestive tract obtained from either vaccinated or control fish.

Surprisingly, the levels of transcription of both IgM and IgT increased in response to vaccination Fig. Therefore, B cells present in the fat tissue surrounding the digestive tract were also responding to oral vaccination.

Levels of transcription of IgM and IgT estimated through real time PCR in control mock-vaccinated with empty alginate microspheres and vaccinated fish. Although different absorption capacities had been reported along different segments of the digestive tract in different teleost species [2] — [4] , their immunological properties had not been properly addressed [1].

In the current work, we have undertaken this task in relation to B cell responses, focusing on B cell mobilization and Ig transcription, and we have demonstrated that concerning B cell responses, the pyloric caeca is the most immunologically active segment of the rainbow trout digestive tract.

Therefore, future studies dealing with immunization in salmonids should take into consideration the immune response elicited in this gut segment. In mammals, IELs are primarily T cells with potent cytolytic and immunoregulatory capacities that because of their properties have been cataloged as a mid-way between adaptive and innate immune responses [27].

Accordingly, previous studies in rainbow trout in which IELs had been isolated from the gut, pointed out that those IELs were T cells [5] , however, in that study, the pyloric caeca segment was not included nor was the search for IgT transcripts. Similarly, B cells can be found as IELs in other mucosal tissues in mammals and for example IELs of human adenoids and tonsils are enriched in B cells [28]. During this activation, Pax5 levels are reduced in part due to the induction of Blimp1 that shifts the Ig expression from membrane to the secreted form [26].

Despite this, in these posterior segments, the transcription of secreted IgM remained almost undetectable. On the other hand, an important level of transcription of secreted IgM was detected in parallel to a Blimp1 - phenotype in the foregut and stomach. The later could suggest the presence of B1 cells in these segments which are known to produce high levels of secreted Ig with low levels of both Blimp1 and Pax5 [29].

Future work in our group will include a further characterization of the phenotypes of these distinct B cell populations isolated from the different segments.

When fish were orally vaccinated, out of the different segments, the pyloric caeca was the only one which significantly responded to the stimulation through an increased IgM, IgT, IgD, membrane IgM, Pax5 and Blimp1 transcription. Moreover, the transcription levels of IgM, IgT, membrane IgM and Blimp1 in the vaccinated individuals strongly correlated with the transcription of the VP2 viral gene indicating that the up-regulations observed for these genes were a direct consequence of vaccine transcription.

Given the fact that Pax5 and Blimp1 have been shown to be negatively correlated and that Pax5 was not correlated to VP2 transcription, we investigated Blimp1 and Pax5 transcription in perfused fish to analyze the response of tissue B cells exclusively, without any input from circulating blood. While Blimp1 levels in the pyloric caeca, midgut and hindgut segments were higher than levels detected in PBLs, the levels of expression of Pax5 in PBLs were times higher than those obtained in any gut segment.

Thus, it seems probable that the up-regulation of Pax5 observed in the pyloric caeca in response to vaccination is a consequence of a higher income of blood into the tissue as a response to vaccination, whereas the up-regulation of Blimp-1 could indicate the maturation of plasma cells locally in response to vaccination.

Our results also reveal the importance of IgM in mucosal responses, challenging the actual line of thought in which IgT seemed to be the Ig subtype mainly responsible for mucosal responses [8]. Our results suggest that both IgM and IgT together respond at an early stage upon mucosal immunization. Finally, our studies have led us to the identification of lymphocyte cells in association with the adipose tissue that surrounds the pyloric caeca. Although the presence of immune cells in diverse adipose structures has been reported in humans and other mammalian models [31] , the immune reactions and how their regulation occur in the various environments within the body have been only marginally appreciated in the past, despite the fact that there is a correlation between the presence of fat-associated lymphoid cells and inflammation in obesity [31].

Adipose tissue in mammals is generally separated into visceral and subcutaneous adipose tissue, being the visceral adipose tissue the one which is metabolically and immunologically more active [32]. In mammals, this visceral fat tissue refers to adipose within the peritoneal cavity, including depots such as the gonadal fat pad, the omentum, and the intestinal mesentery [33]. Fatty structures such as the omentum are enriched in macrophages and B cells [34] , but also possess dendritic cells [35] and NKT cells [36].

In mammals, although B1 B cells predominate in the leukocyte clusters designated as milky spots [37] , B2 conventional responses can be found in the omentum as well. For example, peritoneal immunization with bacteria provoked a strong increase in the number and size of the milky spots [34]. A more recent paper revealed that, after a gammaherpesvirus infection, immune aggregates within the omentum not only expand in size and number but also contain virus-infected cells [39].

Furthermore, in this same study, a germinal-center B cell population appeared in the omentum of infected animals with earlier kinetics and greater magnitude than that observed in the spleen.

In all these experiments, the immunization was performed through intraperitoneal injection; however, not many studies have demonstrated a response of fat-associated immune cells upon oral immunization [38].

In the lungfish, sharks and rays the rectum opens into the cloaca which also receives wastes urine from the kidneys and material from the reproductive organs. In bony fish the rectum reaches the outside environment through the anus, which is normally situated just in front the urinary and reproductive openings.

Most of what is excreted by fish is undigested material and dead bacteria. Fish usually convert nitrogenous wastes into ammonia, which is secreted into the water through the gills. The rest will be formed into urea and pass out through the rectum. In sharks and rays all the nitrogenous wastes are converted into urea.

Single celled archaea , bacteria and fungi that feed on cellulose and other plant products that the fish finds difficult to digest itself and in the process give out excess byproducts such as fatty acids which are useful to the fish.

However in many teleosts it becomes quite reduced and diffuse in the adults. In sharks and rays it is quite distinct from the liver. But in those teleosts wherein it is found, it is often partially embedded in the liver.

The pancreas secretes enzymes such as trypsin attacks proteins , amylases attack carbohydrates and lipases attack fats into the intestines — either through sharing one of the hepatic ducts those belonging to the liver , or through its own pancreatic duct. Is a large organ that play various roles in the fishes body.

It is the site of glycogen storage, it produces a variety of substances — including enzymes that help with the digestion — and it is a major chemical factory producing various hormones as well as numerous other important molecules. The liver is often very large in some sharks and may extend along the body cavity to the cloaca.

The liver usually has two separate lobes, but it may have only one some members of the Salmonidae or even three as in the Mackeral Scomber scomber. The gall bladder is usually found somewhere within the liver.

It secretes substances that attack fats and help them to be broken down. The liver always has at least one — and sometimes as many as eight — ducts leading into the first part of the intestines. In many cases the pancreas will share one of these ducts. We have a lot more articles on fish anatomy here on the Earthlife Web — you can find them here. Love the simplicity of the explanations! I thought anabolism is the synthesis of new material from simpler ones.

Catabolism is the breakdown of materials. In the first part of the article, it says otherwise. Ooh, embarrassing. You are of course correct. Thank you for bringing this mistake to my notice. Great work you have here. Very informative. Just wondering if you have any info on the fish gills? Thank so much.

Stay safe. Hi Lina, Yes we have, if you follow the link to fish at the top of the page and the scroll down to the link for anatomy you will find it.

This may be a bit cumbersome, but there are a lot of pages included in the fish chapter. Here is the link. Your email address will not be published.

Author Recent Posts. Gordon Ramel. Gordon is an ecologist with two degrees from Exeter University. He's also a teacher, a poet and the owner of 1, books. Oh - and he wrote this website. Latest posts by Gordon Ramel see all. Publication types Research Support, Non-U. Gov't Research Support, U. Gov't, Non-P. Research Support, U.