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Members of the Leukocyte Immunoglobulin-like Receptor B (LILRB) family act as negative regulators of myeloid cell activation. LILRBs are Type I transmembrane glycoproteins that function as immunosuppressive receptors; currently identified members of the LILRB family include LILRB1, LILRB2, LILRB3, LILRB4, and LILRB5.

Leukocyte Immunoglobulin-like Receptor B4 (LILRB4)—also known as ILT3, LIR5, CD85K, and HM18—is an inhibitory receptor within the LILR family that is predominantly expressed on normal and malignant human myeloid cells. LILRB4 features two extracellular C2-type Ig domains and three cytoplasmic ITIMs (Immunoreceptor Tyrosine-based Inhibitory Motifs), which recruit phosphatases to mediate downstream signal transduction. LILRB4 is directly involved in regulating MHC-mediated antigen-specific T-cell activation, co-inhibiting CD47-mediated phagocytosis, modulating NK cell activation and immune responses to specific pathogens, and maintaining the stemness of hematopoietic stem cells.

Upon binding to its ligands, LILRB4 becomes activated; this activation subsequently recruits adaptor proteins to its cytoplasmic ITIMs, thereby initiating various signaling cascades. Through these mechanisms, LILRB4 plays a pivotal role in a range of physiological and pathological conditions, including autoimmune diseases, microbial infections, and cancer.

The Jurkat E6.1 Human LILRB4 Effector Reporter Cell Model—effectively simulates the signal transduction process of  LILRB4  *in vivo*. The underlying principle is illustrated in the figure below.

Figure 1. Schematic Diagram of the Jurkat E6.1 Human LILRB4 Effector Reporter Cell Model

Figure 2. Dose response of LILRB4 Blocking antibody in LILRB4 Effector Reporter Cell(C5) With  ANGPTLx TCR Activitor CHO(C1)  and  APOE TCR Activitor CHO(C1).

Cell Passage Procedures

1.This cell line grows in suspension.
2.Upon receipt, cells should be thawed immediately or stored in liquid nitrogen until use.
3.Before thawing, pre-warm the water bath and culture medium to 37 °C, and prepare a small amount of dry ice.
4.Remove the cryovial from storage and transport it to the cell culture laboratory on dry ice.
5.Rapidly thaw the cells in a 37 °C water bath. Once the cells are completely thawed, spray the cryovial with 70% ethanol for disinfection and transfer it to a biosafety cabinet.
6.Add 10 mL of pre-warmed culture medium into a 15 mL centrifuge tube. Transfer the contents of the cryovial into the tube and centrifuge at 1000 rpm for 5 minutes.
7.Carefully discard the supernatant. Resuspend the cell pellet in 5 mL of pre-warmed culture medium by gentle pipetting. Immediately perform cell counting and adjust the cell density to 3–6 × 10⁵ cells/mL based on the counting results, then transfer the cells into a culture flask.
8.Count the cells every 1–2 days. When the cell density exceeds 1 × 10⁶ cells/mL, passage the cells promptly or add fresh culture medium. Maintain the cell density between 2 × 10⁵ and 1 × 10⁶ cells/mL.

Suspension Cell Cryopreservation Procedure:

1.Collect 8 × 10⁶ cells, centrifuge, and discard the supernatant.
2.Add 1 mL of cell freezing medium (90% FBS + 10% DMSO) and gently pipette to mix thoroughly. Transfer the suspension into a cryovial.
3.Immediately place the cryovial into a controlled-rate freezing container (Nalgene 5100-0001), fill with isopropanol up to the indicated level, and store at −80 °C.
4.After 24 hours, transfer the cryovial to liquid nitrogen for long-term storage.