Genomics and Applied Biology 2018, Vol.9, No.9, 56-61
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(Jaso-Friedmann et al., 2004). Previous studies have shown that NCCRP-1 is a marker receptor of NCC (Evans et
al., 1996), but there are very few reports on the study of fish NCC by immunohistochemical technique. Most of
the previous studies have obtained the expression of the receptor among different tissues and organs by qPCR
method (Cai et al., 2013), or verified its existence by flow cytometry after Percoll (Zhou, 2012) or Ficoll (Evans et
al., 1984) separation. The relative expression of NCC from various organs and the percentage of NCC in the
whole tissue of cells can be obtained by the above methods. However, the existence and distribution of NCC in
tissues cannot be directly observed.
In this study, brain, head-kidney, liver and spleen were selected to carry out immunohistochemical experiments.
By observing slices, it was found that NCC was distributed in all the above organs, which was consistent with the
reported results. The brain plays an irreplaceable role in the process of life as central nervous organs of animals
(Robinson and Meyer, 1966). Therefore, safety and steady state play important roles in the exercise of its function.
However, we made continuous slices of the brain and the results showed that the number of NCC in the brain was
significantly lower than that in immune organs, which was not consistent with the expectation of experiment. A
large number of studies have confirmed that there is indeed a blood-brain barrier in fish, although fish belong to
lower vertebrates (Stratman et al., 2017), which makes it difficult for foreign microorganisms to enter the brain. In
the results of our experiment, there was still a part of NCC in the brain, because in addition to non-specific killing
of foreign antigens, NCC could also kill endogenous and exogenous tumor cells (Graves et al., 1985). This part of
NCC in the brain might be related to its timely killing of own tumor cells and the prevention of canceration of
central nervous cells. Moreover, some studies have shown that some bacteria, such as Streptococcus agalactiae,
can enter the cranial cavity with blood after being swallowed by macrophages, thus causing diseases (Schuchat,
1998). In the following experiments, we can use pathogens to stimulate fish, select a time point to sample the
brain, and observe the number and distribution of NCC in the brain stimulated under the pathogens to further
explore the characteristics of NCC.
The widespread distribution of NCC in head-kidney and spleen, which are important immune organs of fish
(Wood and Cheers, 1985; Mulero et al., 1994), once again highlights its importance. The head kidney and liver not
only bear the specific immunity of teleost fishes, but also play an extremely important role in nonspecific
immunity at the early stage of pathogen stimulation. It could be observed from the slices that NCC was
aggregated and distributed on the mucosal surface of the internal lumen of the organ, which indicated that NCC
would carry out killing on the mucosal surface immediately when the fish was infected and the pathogen spread
with body fluids. A large number of reports have shown that the mucosa of teleost fish also plays an important role
in host immunity (Rombout et al., 2014), and the results of this study were consistent with the existing literature.
In addition to the intraluminal mucosa inside the organ, the gills (Somamoto et al., 2015) and intestines
(Georgopoulou and Vernier, 1986) of fish are also responsible for mucosal immunity. Next, the above tissues
would be sectioned to observe the number and distribution of NCC. Meanwhile, NCCRP-1 is also distributed in
the liver of
Oreochromis niloticus
. Interestingly, although the liver is not the main immune organ of teleost fishes,
it was also confirmed that NCCRP-1 receptor existed in the liver of
Oreochromis niloticus
,
Lutjanus sanguineus
,
Onchorhynchus mykiss
,
Cyprinus carpio
and other species (Evans et al., 1996; Seppola et al., 2007; Fischer et al.,
2013). It was speculated that the liver, as the detoxifying organ of fish (Cao, 2008), might be often stimulated by
exogenous, and the probability of forming cancer cells might be higher than that in other organs. Cancer cell is
just one of the target cells of NCC. Timely and effective phagocytosis of cancer cells would play an important role
in maintaining the homeostasis of the environment in fish.
In this study, high purity NCC in the head-kidney tissue of
Oreochromis niloticus
was obtained by Percoll
separation method. NCC positive signals were obtained through HRP and FITC antibody markers. Compared with
other published fish NCC, the NCC of
Oreochromis niloticus
also had the marker receptor protein, which proved
that NCCRP-1 was a kind of marker receptor protein of NCC once again. Compared with immunohistochemical
staining in tissues, this experiment excluded nonspecific antibody markers of other kinds of cells in tissues to
further determine the experimental results.
