Illustration of GRP78 and IL-34 interaction on a cell membrane, symbolizing immune response regulation.

Cell Surface Signaling: How a Protein Called GRP78 Regulates Immune Responses

Theo Raines in Health & Wellness December 2025 • 4 min read.

"Researchers uncover how GRP78 influences IL-34's role in cell differentiation, potentially opening new avenues for autoimmune disease treatments."

Our immune system is a complex network of cells and signals that work together to protect us from harm. Among the many players in this system are cytokines, which act as messengers to regulate immune responses. Interleukin-34 (IL-34) is one such cytokine, and it shares a receptor, called colony-stimulating factor-1 receptor (CSF-1R), with another important cytokine, CSF-1.

Researchers have been particularly interested in understanding how IL-34 works in the body, especially its role in the differentiation of specific types of immune cells. One area of focus has been on a novel type of monocytic cell (FDMC) whose differentiation depends on CSF-1R signaling through the IL-34 produced from a follicular dendritic cell line (FL-Y).

A recent study published in the Journal of Biological Chemistry sheds new light on how IL-34 functions, revealing that a protein called GRP78 plays a critical role in regulating IL-34's activity on the cell surface. This discovery has implications for our understanding of immune responses and could pave the way for new treatments for autoimmune diseases.

What is the role of cell surface IL-34 in FDMC differentiation?

Illustration of GRP78 and IL-34 interaction on a cell membrane, symbolizing immune response regulation.

To confirm the importance of IL-34 in FDMC differentiation, the researchers first created FL-Y cells that lacked the ability to produce IL-34. Using CRISPR/Cas9 technology, they knocked out the Il34 gene in FL-Y cells, and they confirmed that these IL-34 KO FL-Y cells were unable to induce FDMC differentiation.

To investigate how IL-34 signals to induce FDMC differentiation, the researchers used a transwell culture system to separate FL-Y cells from FDMC precursor cells. They found that direct cell-cell contact was required for FDMC differentiation, suggesting that IL-34 on the surface of FL-Y cells, rather than secreted IL-34, was responsible for the effect. They confirmed with flow cytometric analysis using an anti-IL-34 antibody that IL-34 was expressed on the FL-Y cell surface.

To identify the molecule(s) regulating IL-34 expression on the FL-Y cell surface, the researchers established an FL-Y cell line expressing twin-Strep-tagged IL-34 (FL-Y-IL-34-Nst). The twin-Strep-tag allowed them to purify IL-34 and any proteins that interacted with it. Mass spectrometry analysis and pull-down assays revealed that IL-34 was associated with the molecular chaperone GRP78 in the plasma membrane fraction of FL-Y cells. Further experiments showed that:

GRP78-heterozygous FL-Y cells expressed lower levels of IL-34 on their cell surface.
These cells exhibited a reduced ability to induce FDMC differentiation compared with the original FL-Y cells.

These results indicate that GRP78 plays a critical role in regulating IL-34 expression on the FL-Y cell surface and that this interaction is important for FDMC differentiation.

Implications and Future Directions

This study provides valuable insights into the complex mechanisms that regulate immune responses. By identifying GRP78 as a key regulator of IL-34 cell surface expression, the researchers have opened up new avenues for understanding and potentially treating autoimmune diseases. Further research is needed to fully elucidate the role of GRP78 in IL-34 signaling and to explore the therapeutic potential of targeting this interaction.

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Everything You Need To Know

What is the role of IL-34 in FDMC differentiation?

IL-34, a cytokine, is crucial for FDMC differentiation. Researchers found that IL-34 on the surface of FL-Y cells, specifically, is responsible. When FL-Y cells lacked IL-34, they couldn't induce FDMC differentiation. This highlights the direct and essential role of cell surface IL-34 in the process. The differentiation of FDMC is dependent on CSF-1R signaling through the IL-34 produced from a follicular dendritic cell line (FL-Y).

How does GRP78 influence IL-34's function?

GRP78 is a protein that regulates the expression of IL-34 on the cell surface. This interaction between GRP78 and IL-34 is critical for FDMC differentiation. Experimental results showed that FL-Y cells with lower levels of GRP78 expressed lower levels of IL-34 on their cell surface, which reduced their ability to induce FDMC differentiation. This emphasizes the importance of GRP78 in mediating IL-34's function and its impact on immune cell development. The molecular chaperone GRP78 in the plasma membrane fraction of FL-Y cells.

What are the implications of this research for autoimmune diseases?

Autoimmune diseases occur when the immune system mistakenly attacks the body's own cells. GRP78's role in regulating IL-34, which influences immune cell differentiation, suggests it could be a therapeutic target. By understanding how GRP78 affects IL-34, scientists may find ways to modulate immune responses and potentially treat autoimmune conditions. The discovery has implications for understanding and potentially treating autoimmune diseases.

What is the significance of cytokines like IL-34 in immune responses?

Cytokines like IL-34 are signaling molecules that regulate immune responses by acting as messengers within the immune system. IL-34, in particular, interacts with the CSF-1R to influence immune cell differentiation. The research emphasizes how understanding the interactions of cytokines like IL-34, and the factors that regulate them, provides insights into the complexities of immune system function. CSF-1R shares a receptor with another important cytokine, CSF-1.

What are FL-Y cells and why were they used in this research?

FL-Y cells are a follicular dendritic cell line used in this study. These cells were used to study how IL-34 functions. Researchers used FL-Y cells to understand the mechanism of IL-34 and its involvement in FDMC differentiation. The study used FL-Y cells that lacked the ability to produce IL-34 to confirm the importance of IL-34 in FDMC differentiation. To investigate how IL-34 signals to induce FDMC differentiation, the researchers used a transwell culture system to separate FL-Y cells from FDMC precursor cells.