CD33

Overview

CD33 is a myeloid-associated cell-surface protein that functions as an inhibitory receptor in immune signaling. It is best known for its expression on cells of the myeloid lineage, including monocytes and macrophages, and for its role in dampening cellular activation through intracellular inhibitory motifs. In the context of signaling, CD33 can transmit inhibitory signals after phosphorylation of its immunoreceptor tyrosine-based inhibitory motifs (ITIMs), leading to recruitment of phosphatases such as SHP-1/2 and reduced myeloid cell activation.

Biomedically, CD33 is relevant in both hematologic and neurodegenerative disease research. In acute myeloid leukemia, CD33 is a commonly studied surface marker on blasts and is used in disease characterization. In the central nervous system, CD33 has attracted attention because genetic polymorphisms that reduce its expression have been associated with protection in Alzheimer’s disease-related research, consistent with a role in regulating neuroinflammation and microglial function. Its functional relationship with Triggering receptor expressed on myeloid cells 2 (TREM2) has also made it a focus of studies examining innate immune mechanisms in Alzheimer's disease.

Focus of Latest Publications

Recent publications have continued to position CD33 as a biologically important regulator of myeloid-cell signaling in both neurodegeneration and immunosuppression.

One study on the mechanisms of increased Alzheimer's disease pathology with R47H and R62H TREM2 variants noted that genetic polymorphisms reducing expression of the functionally related protein CD33 are protective. This supports the broader concept that CD33 contributes to disease-relevant immune regulation in the brain, where altered myeloid signaling may influence pathology alongside TREM2. The study context links CD33 to Alzheimer’s disease risk biology rather than to a direct therapeutic intervention, emphasizing its role as a genetically and functionally relevant target in neuroinflammatory pathways.

A second publication, focused on therapeutic potential in a rat model of scopolamine-induced cognitive impairment, explicitly stated that CD33 plays a significant role in regulating immune responses, particularly in the central nervous system, and has been implicated in the progression of Alzheimer's disease. In that work, CD33 was part of a broader mechanistic framework involving neuroinflammation, sialylation, acetylcholinesterase, Beta amyloid, oxidative stress markers such as MDA content and NO₂, and interventions including donepezil, L-scopolamine, glutathione, and carboxy methyl cellulose. Although the study centered on a nanocarrier-based therapeutic strategy rather than CD33-directed treatment, CD33 was discussed as a relevant immune regulator in the disease process being modeled.

A third study, the crystal structure of the CD33/Fab-10C8 complex, provided direct structural insight into antibody antagonism in HBV-induced immunosuppression. The reported mechanism indicated that the interaction induces ITIM phosphorylation and SHP-1/2 recruitment, dampening myeloid cell activation. This is important because it clarifies how CD33 can be antagonized by an antibody-based approach, with structural data explaining how binding may alter inhibitory signaling. The study therefore connects CD33 to immune suppression in a viral disease context and shows how antibody 10C8 can modulate its function.

A fourth publication examined CD135 (FLT3 receptor) expression as a prognostic indicator in de novo acute myeloid leukemia and reported that the high-CD135-expression group had significantly lower CD34 surface expression and higher CD33 expression on AML blasts. This reinforces the use of CD33 as a phenotypic marker in leukemia biology and highlights its association with blast immunophenotype in clinical hematology. In this setting, CD33 was not the primary prognostic variable, but it was part of the surface-marker profile used to characterize AML cells and interpret disease subgroups, including analyses supported by a prognostic nomogram.

Key Publications

Jun Mechanisms of increased Alzheimer's disease pathology with R47H and R62H TREM2 variants. (Acta neuropathologica, 2026, PMID 42298074): "Genetic polymorphisms reducing expression of the functionally related protein CD33 are protective."
Jun Therapeutic Potential of Stearylamine-Conjugated Phenylboronic Acid-Modified Nanocarriers of 4-Allyl Pyrocatechol in Modulating Sialylation and Neuroinflammation in Scopolamine-Induced Cognitive Impairment in the Rat Model. (Molecular pharmaceutics, 2026, PMID 42267754): "CD33 plays a significant role in regulating immune responses, particularly in the central nervous system, and has been implicated in the progression of Alzheimer's disease."
May Crystal structure of the CD33/Fab-10C8 complex elucidates the mechanism of antibody antagonism in HBV-induced immunosuppression. (Journal of biomedical science, 2026, PMID 42215976): "This interaction induces ITIM phosphorylation and SHP-1/2 recruitment, dampening myeloid cell activation."
May CD135 (FLT3 receptor) expression as an indicator of prognosis in patients with de novo acute myeloid leukemia. (Annals of hematology, 2026, PMID 42067641): "The high-CD135-expression group had significantly lower CD34 surface expression (p=0.003) and higher CD33 expression (p=0.014) on AML blasts."