Blood cell

Summary

A blood cell, also called a hematopoietic cell, hemocyte, or hematocyte, is a cell produced through hematopoiesis and found mainly in the blood. Major types of blood cells include red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes). Together, these three kinds of blood cells add up to a total 45% of the blood tissue by volume, with the remaining 55% of the volume composed of plasma, the liquid component of blood. Red blood cells Red blood cells or erythrocytes, primarily carry oxygen and collect carbon dioxide through the use of hemoglobin. Hemoglobin is an iron-containing protein that gives red blood cells their color and facilitates transportation of oxygen from the lungs to tissues and carbon dioxide from tissues to the lungs to be exhaled. Red blood cells are the most abundant cell in the blood, accounting for about 40-45% of its volume. Red blood cells are circular, biconcave, disk-shaped and deformable to allow them to squeeze

Official source

https://en.wikipedia.org/wiki/Blood_cell

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The use of tractable model organisms such as Drosophila melanogaster and the powerful genetic tools they offer has contributed significantly to recent advances in comprehension of innate immunity, notably phagocytosis. To date, several phagocytic transmembrane receptors, opsonins, and ligands have been discovered in Drosophila melanogaster. Many of them belong to the Nimrod family, which includes both secreted and transmembrane proteins containing several NIM repeats. Genetic and biochemical studies have revealed the roles of transmembrane Nimrod receptors such as Draper, Simu and Eater in phagocytosis. However, the function of the five secreted Nimrod members, the Nimrod B proteins, remains unstudied. The goals of my thesis were to characterize the function of the secreted Nimrod B proteins using newly generated CRISPR-Cas9 null mutations, focusing on NimB5, NimB4, and NimB1 genes. In this work, we first found that the secreted protein, NimB5, is produced in the fat body upon nutrient scarcity downstream of metabolic sensors and ecdysone signaling. We provide evidence that NimB5 binds to hemocytes to down-regulate their proliferation and adhesion. Blocking this signaling loop results in conditional lethality when larvae are raised on a poor diet due to excessive hemocyte numbers and insufficient energy storage. This pointed to a role of NimB5 in the allocation of resources to blood cells, tailoring the investment in the immune system to metabolic resource availability.In the second part of this thesis, we analyzed the function of NimB4 to reveal its crucial role in clearance of apoptotic cells. NimB4 is expressed by macrophages and glial cells, the two main types of phagocytes in Drosophila. Our study points to a role of NimB4 in phagosome maturation, more specifically in the fusion between the phagosome and lysosomes. We propose that similar to bridging molecules, NimB4 binds to apoptotic corpses to engage a phagosome maturation program dedicated to efferocytosis. Finally, in the last part of the thesis, we present preliminary results on the role of NimB1 in the Drosophila immune system. NimB1 is expressed mainly in hemocytes and regulates hemocyte number. Additionally, NimB1 shares several characteristics with NimB4, notably the ability to bind to apoptotic cells. As such, we hypothesize that it could play a similar function in the phagocytosis of apoptotic cells. However, the exact role of NimB1 in phagocytosis is still unclear, and additional work is necessary to understand if NimB1 plays a role in the uptake of apoptotic cells or phagosome maturation. Collectively, this thesis has revealed that the NimB proteins play specific roles in efferocytosis or in blood cell number regulation. Thus, this work extended our knowledge on the Drosophila cellular immune response by providing new insight on the conserved Nimrod family of proteins.

EPFL2022

The analysis of circulating tumor cells (CTCs) from the blood of cancer patients promises a better understanding of metastasis formation and tumor phenotypes. CTCs are rare (there is 1 CTC in 1 billion of circulating blood cells) and therefore challenging to isolate. Recently developed highly sensitive microfluidic platforms made a leap forward in trapping these cells efficiently. This work focused on the development of a microfluidic platform that specifically captures prostate cancer cells from a whole blood sample. The versatility of the system was exploited by tethering different capturing antibodies on the microchip surface. Circulating prostate tumor cells were successfully recognized with the microfluidic chip. Furthermore, the platform was enhanced to carry out proliferation assays of captured cells directly on the chip, using hydrogel as a three-dimensional cell culture matrix. Although further improvements regarding the on-chip proliferation assay need to be done, the potential benefit of a functional readout promises new insights in cancer progression that can be translated to advanced cancer staging or prognostic tools.

2011

Adult Drosophila Lack Hematopoiesis but Rely on a Blood Cell Reservoir at the Respiratory Epithelia to Relay Infection Signals to Surrounding Tissues

Bruno Lemaitre, Elodie Julie Virginie Ramond

The use of adult Drosophila melanogaster as a model for hematopoiesis or organismal immunity has been debated. Addressing this question, we identify an extensive reservoir of blood cells (hemocytes) at the respiratory epithelia (tracheal air sacs) of the thorax and head. Lineage tracing and functional analyses demonstrate that the majority of adult hemocytes are phagocytic macrophages (plasmatocytes) from the embryonic lineage that parallels vertebrate tissue macrophages. Surprisingly, we find no sign of adult hemocyte expansion. Instead, hemocytes play a role in relaying an innate immune response to the blood cell reservoir: through Mid signaling and the Jak/Stat pathway ligand Upd3, hemocytes act as sentinels of bacterial infection, inducing expression of the antimicrobial peptide Drosocin in respiratory epithelia and colocalizing fat body domains. Drosocin expression in turn promotes animal survival after infection. Our work identifies a multisignal relay of organismal humoral immunity, establishing adult Drosophila as model for inter-organ immunity.

CELL PRESS2019

EPFL2022