Anti-Human CD11b – Purified in vivo PLATINUM™ Functional Grade

Clone ICRF44, a mouse monoclonal antibody targeting human CD11b (integrin alpha M, Mac-1, CR3), is primarily used in in vitro applications such as flow cytometry and immunohistochemistry for detecting and studying human CD11b-expressing cells. However, its common in vivo applications in mice are more nuanced and involve use in "humanized" mice models, which are often referred to as Human Immune System (HIS) mice. These models allow researchers to study human immune responses in a preclinical setting.

In such models, ICRF44 can be used to:

• Target CD11b-expressing human cells in vivo, particularly when studying immune responses in HIS mice.
• Block adhesion and stimulate cytokine release from monocytes, which can be beneficial in understanding immune cell interactions within a humanized mouse environment.
• Assess the role of CD11b in inflammation and immune responses, potentially aiding in the development of immunotherapies.

However, detailed descriptions of specific in vivo applications in mice are limited compared to in vitro uses.

Commonly Used Antibodies and Proteins Alongside ICRF44 in the Literature

ICRF44 is a widely used monoclonal antibody that recognizes human CD11b (integrin alpha M, Mac-1, CR3). In experimental and clinical research, ICRF44 is often paired with other antibodies and proteins to gain a comprehensive understanding of immune cell phenotypes, activation states, and functional interactions.

Key Companion Antibodies

• Anti-CD18: Frequently used alongside ICRF44 to assess the expression and function of the complete Mac-1 complex (CD11b/CD18), since CD11b forms a heterodimer with integrin beta-2 (CD18) to create this receptor. Co-staining with anti-CD18 helps determine whether the Mac-1 complex is correctly formed on the cell surface.
• Anti-CD14: Often used to distinguish monocytes and macrophages from granulocytes and other myeloid cells, as CD14 is a marker for monocytes/macrophages, while CD11b (ICRF44) is also expressed on granulocytes and activated lymphocytes.
• Anti-Lymphocyte Markers (e.g., CD3, CD4, CD8, CD19, CD56): Commonly included to identify and gate on lymphocyte subsets, especially when studying the minor CD11b+ lymphocyte populations.
• Activation Markers (e.g., CD69, HLA-DR, CD25): Sometimes used with ICRF44 to assess the activation state of monocytes, granulocytes, or rarely, lymphocytes.
• NK Cell Markers (e.g., CD56, CD16): Used to identify and analyze CD11b+ NK cell subsets.
• Microglial Markers (e.g., TMEM119, P2RY12): When studying nervous tissue, ICRF44 is often paired with microglia-specific markers, as CD11b is a commonly used but not exclusive microglial marker.
• Cross-Species Markers: ICRF44 can cross-react with CD11b in non-human primates (rhesus, cynomolgus macaque, baboon); thus, species-specific pan-leukocyte markers are sometimes used in comparative studies.

Commonly Used Proteins and Receptors

• Ligands for CD11b/CD18: The Mac-1 complex (CD11b/CD18) is a receptor for several proteins, including ICAM-1 (CD54), ICAM-2 (CD102), ICAM-3 (CD50), iC3b (C3b), fibrinogen, heparin, and Factor X. In functional assays, these proteins may be used to study CD11b-mediated adhesion, phagocytosis, or signaling.
• Complement Proteins (e.g., C3b/iC3b): Used in phagocytosis or opsonization assays, leveraging CD11b’s role as complement receptor 3 (CR3).
• Fc Receptors (e.g., CD16, CD32, CD64): While not direct targets of ICRF44, these are often studied alongside CD11b in assays involving phagocytosis, antibody-dependent cellular cytotoxicity, or immune complex clearance.

Typical Use-Cases

• Multiparameter Flow Cytometry: ICRF44 is commonly included in panels for immunophenotyping, where it is combined with markers for cell lineage, activation, and function.
• Functional Assays: In vitro adhesion, migration, or phagocytosis assays often use ICRF44 in combination with the Mac-1 (CD11b/CD18) ligands mentioned above.
• Cross-Species Studies: When validating animal models, ICRF44 is used with species-specific antibodies to confirm CD11b expression patterns.

Summary Table

Conclusion

In the literature, ICRF44 is most frequently used alongside anti-CD18 (for Mac-1 complex analysis), anti-CD14 (for monocyte/macrophage identification), lymphocyte and NK cell markers (for subset analysis), and various ligands (ICAMs, C3b, fibrinogen) for functional studies. The choice of companion antibodies and proteins depends on the specific research question—whether immunophenotyping, functional analysis, or cross-species validation.

The monoclonal antibody clone ICRF44 is widely used in scientific literature to specifically target human CD11b (integrin αM, part of Mac-1/CR3), a key leukocyte surface receptor involved in immune responses, cell adhesion, and migration. Below are the main findings and applications cited for ICRF44:

• Specificity and Reactivity: Clone ICRF44 binds human CD11b, which is expressed on monocytes, granulocytes, macrophages, natural killer (NK) cells, and some lymphocytes. It is reported to cross-react with CD11b from several non-human primates (e.g., chimpanzee, baboon, rhesus monkey).

• Functional Blocking: ICRF44 is used to inhibit heterotypic adhesion of granulocytes (especially in response to fMLP), block granulocyte activation, and prevent neutrophil aggregation—demonstrating its value in studying cell-cell and cell-matrix adhesion mechanisms.

• Signaling and Activation: Studies using ICRF44 show that CD11b/Mac-1 receptor clustering can initiate pro-inflammatory responses, cytokine release, and promote leukocyte recruitment, highlighting its role in immune cell activation and inflammation.

• Tissue and Cell Profiling: ICRF44 is a standard marker for flow cytometry and immunofluorescence to identify and quantify CD11b⁺ cells in blood or tissue samples. It is effective for human samples but not compatible with formalin-fixed paraffin-embedded (FFPE) tissues.

• Mechanistic Studies: The antibody has been used in advanced imaging (e.g., total internal reflection fluorescence microscopy) to analyze receptor clustering and intracellular signaling in live cells.

• Functional Assays: ICRF44 is employed in assays that measure granulocyte and monocyte functional responses such as adhesion, phagocytosis, and stimulation, furthering understanding of immune cell dynamics.

Notable Citations:

• Rezzonico et al., Blood (2001): Showed stimulation of monocytes using ICRF44.
• Marsik et al., Shock (2003): Demonstrated use in flow cytometry for granulocyte analysis.
• Comprehensive reference works: Leucocyte Typing IV (Knapp, 1989) and The Leukocyte Antigen Facts Book (Barclay et al., 1997) describe ICRF44 specificity and effects.

Key limitations:

• ICRF44 does not work with FFPE tissue sections, restricting its use in certain histopathological workflows.
• It is specifically designed for human (and some primate) CD11b, not mouse or other species.

The recurring themes in literature are functional blockade of CD11b/Mac-1, use in cell differentiation and immune response studies, and high utility for flow cytometry and immunofluorescence methodologies in immunology and hematology research.

There is no standardized or widely published in vivo dosing regimen for clone ICRF44 (anti-human CD11b monoclonal antibody) across different mouse models; most available data reflect its use in in vitro applications or detection of human CD11b+ cells in immunohistochemistry and flow cytometry.

Context and Supporting Details:

• Primary Usage: Clone ICRF44 is mostly employed to detect or block human CD11b molecules (MAC-1/CR3) in in vitro assays or on human cells in engineered mouse models, rather than as a therapeutic agent dosed in live animals.
• Dilution Guidelines (Immunohistology): Where mouse tissues are used for immunohistochemical detection (e.g., after xenografting human cells into immunodeficient mice), recommended antibody dilutions range from 1:100 to 1:1000, but these refer to in vitro staining protocols, not systemic dosing.
• Species Cross-Reactivity: The antibody is designed for human CD11b and shows documented cross-reactivity with some non-human primates (cat, cynomolgus monkey, baboon, rhesus monkey), but mouse CD11b detection is not a typical application.
• Research and Manufacturers’ Notes: Both product manufacturers (Leinco, BioLegend, Bio-Rad) and published literature emphasize that working conditions—including any attempt at in vivo dosing—may vary widely by species and application, and must be empirically optimized.
• Humanized Mouse Models: In humanized mouse models (immunodeficient mice engrafted with human immune cells), clone ICRF44 would be used for cell detection or targeting human monocytes/macrophages, not for broad systemic dosing. The details of actual dosing protocols in such settings, if used for functional blockade or depletion, are not standardized or published, and would need to be determined empirically depending on the desired biological effect and the specific mouse model.

Additional Information:

• Alternate Meanings: Some confusion may arise with dosing schedules for unrelated therapeutics (e.g., alpha interferon in ICR mice), but this is not directly relevant to clone ICRF44.
• No Published Systemic Dosing Regimens: Searches of primary vendors and the scientific literature indicate no consensus or recommended in vivo dose for clone ICRF44 across various mouse models; researchers typically establish their own dose-escalation or efficacy studies if attempting antibody administration.

In summary, clone ICRF44 is generally used for detection of human CD11b+ cells in mouse samples, especially in humanized mice, and there is no standard or published systemic dosing regimen across mouse models; any in vivo application must be empirically optimized for each experiment.