The development and differentiation of NK cells are highly noted in recent years.In addition to the peripheral blood,spleen and bone marrow,the liver,lymph nodes and thymus are also considered as important organs for differentiation of NK cell precursors(NKPs).Human NK cell subset CD56bright is enriched in secondary lymphoid tissues and non-lymph tissues;NK subset cell CD56dim can migrate to peripheral inflammatory region.Activating receptors on NK cells include cytokine receptors,integrin receptors,natural cytotoxic receptors,immunoglobulin-like killer receptors,and many new receptors and ligands different from the aforementioned receptor families.In the process of tumor progression,NK cells can directly recognize malignant cells via "internal recognition" and be activated;they can also be activated by accessory cells such as monocytes,macrophages and dentritic cells.DC cells can trigger the activation of NK cells,in which the reverse signal transduction of IL-15R-IL-15 plays an important role.Great progression has been made in NK cell-based immunotherapy of tumor,in particular there are many new ways in NK cell innate recognition-based tumor biotherapy.

Type Ⅱ innate lymphoid cells is an emerging family of innate lymphocytes mainly distributed in mucosal tissues such as the lungs,intestines,skin,etc.These cells are capable of producing Th2-type cytokines including IL-5 and IL-13 in response to IL-25 and IL-33.ILC2s has attracted much attention for its important roles in anti-infection immunity and allergic diseases in respiratory tract.Studies have shown that ILC2s represented a crucial source of Th2-type cytokines and could regulate the adaptive immune response in allergic airway diseases.Meanwhile,ILC2s was able to fulfill vital functions in parasite clearance, anti-virus infection and subsequent tissue repair.Therefore,research in ILC2s phenotype,development and function has great practical significance.This paper reviews the definition, classification, developmental regulation of ILC2s with a particular focus on its role in respiratory mucosal homeostasis and lung-related diseases.

As the passage of environmental atmosphere entering the body,the respiratory tract suffers persistent challenge from foreign substances.The mucosal immune system of the respiratory tract is the main defense line against the invasion of pathogens,which needs to distinguish not only beneficial and detrimental materials but also resident and pathogenic bacteria.Because the knowledge about respiratory mucosal immunity is limited,the immunopathologic mechanisms of related diseases such as asthma,acute lung injury, chronic obstructive pulmonary disease, and respiratory infection need investigation.The study about the immune features of the respiratory tract not only contributes to the prevention and treatment of respiratory disease but also provides ideas for the development and design of new vaccines and medicines.

Natural killer cells are the key effector cells in innate immune response,playing the role in pathogen clearance and tumor immunosurveillance by cytokine secretion and cytotoxicity.Hematopoietic stem cells go through developmental intermediates to generate mature NK cells under the progressive regulation of extrinsic factors and intrinsic factors.In the past thirty years, great progresses have been made in the developmental progress,niches,regulation of NK cells and the relationship between NK cells and dis-eases.In this review,we will discuss in detail the molecular mechanisms of NK cell development and the diseases caused by functional compromise of NK cells.

NKR and TLR are most important receptor superfamilies in innate immunity and act as first line of host defense against infection. Those receptors exert peculiar recognition mechanisms to sense danger signals and distinguish infectious nonself from noninfectious self. More importantly, they coordinate and regulate each other and therefore play major roles in initiation of innate immunity and also help to direct adaptive immune responses. The importance of recognition and interaction of those receptors are highlighted. The precise mechanisms can be harnessed to aid the rational design of therapy against infection, inflammation, cancer or autoimmune diseases.

We used MTT assay to test the cellular cytotoxicity ( NK, LAK, CTL, Macrophage), cytokine activities ( 1L-1, 1L-2, 1L-6, TNF), proliferation of lymphocytes and chemosensitivity of tumor cells, and compared it with radioactive isotope assay. The results showed that the MTT assay may be used to test the cellular cytotoxicity, cytokine ac-tivity, proliferation of lymphocytes and chemosensitivity of tumor cells. We think it is a simple, rapid, economic and safety method.

Natural killer (NK) cells have long been considered the only representative of lymphocyte lineages among the innate immune system ,but recent studies have revealed that several types of innate lymphoid cells ( ILC ) exist in both humans and mice.These newly identified ILC populations were mainly distributed at mucosal barriers ,regardless of their rarity ,they play important roles in the defense against pathogens and in the maintenance of tissue or organ homeostasis .In the early stages of ILC development ,a common ILC lineage-restricted progenitor exists and under the control of different transcription factors ,the progenitor can later give rise to different ILC subsets with distinct phenotypes and functions.Different ILC subsets exhibit distinct cytokine secretion profiles ,based on the categorization of helper T cell subsets , ILC family has been further classified into three groups.The finding of diverse ILC extremely enriches the content of innate immunity ,and also provides new insights into links between innate and adaptive immunity .

thymus.It is not clear why and how these distribution exist,which is possibly correlated to recruitment,homing,subset,and microenvironment of NK cells in each tissue or organ.

A new NK cell subset with antigen presentation function was recently found and called as interferon-producing killer dendritic cells (IKDC cells).These cells co-express surface markers of NK cells and DCs;functionally,they can secrete interferons,kill target cells and have antigen-presenting ability.IKDCs extensively exist in almost all lymphoid tissue or organs with similar phenotype,but recent studies indicated that IKDCs were developmently not from DC cells but from NK cells,the conclusion of which is still in its early stage.The discovery of IKDC will be help to understand the link between innate and adaptive immunity.

Recent reports have indicated that NK cells may have the function of immunological memory in common with cells of the adaptive immune system."Memory" NK cells move through the four phases of the adaptive immune response — proliferation,contraction,memory and recall which was similar to the T-cell responses."Memory" NK cells have special phenotypes.During MCMV infection,"memory" NK cells showed a greater expression of Ly49H,KLRG1,CD43 and Ly6C,and a decreased expression of CD27.In hapten (DNFB)-induced contact hypersensitivity model,the sorted liver NK cell subsets with the phenotype of Thy-1+Ly49C-I+ had the transferable memory activity,occupying around 10% of hepaedtic NK cells.These Ly49H+"memory" NK cells might produce more IFN-gamma ex vivo in response to plate-bound antibody against NK1.1 or Ly49H.Degranulation by Ly49H+ "memory" NK cells was also enhanced,as assessed by CD107a expression after ex vivo stimulation with anti-NK1.1."Memory" NK cells may move through the same migratory routes and adhesion pathways during the priming and effector phases of DNFB-primed Rag2-/-mice as conventional T cells of normal mice.Until now,it is not clear about the requirements for the triggering,regulation and maintenance of NK cell memory,but it is absolutely clear that "Memory" NK cells must play important role in host defense against pathogens.