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Updated: Apr 28, 2026
Isolation, Transfection, and Culture of Primary Human Monocytes
Published on: December 16, 2019
CD4 ligation on human blood monocytes triggers macrophage differentiation and enhances HIV infection
Anjie Zhen1, Stephan R Krutzik2, Bernard R Levin1
1Division of Hematology/Oncology, Department of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, California, USA UCLA AIDS Institute, Department of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, California, USA.
Unlabelled:
A unique aspect of human monocytes, compared to monocytes from many other species, is that they express the CD4 molecule. However, the role of the CD4 molecule in human monocyte development and function is not known. We determined that the activation of CD4 via interaction with major histocompatibility complex class II (MHC-II) triggers cytokine expression and the differentiation of human monocytes into functional mature macrophages. Importantly, we determined that CD4 activation induces intracellular signaling in monocytes and that inhibition of the MAPK and Src family kinase pathways blocked the ability of CD4 ligation to trigger macrophage differentiation. We observed that ligation of CD4 by MHC-II on activated endothelial cells induced CD4-mediated macrophage differentiation of blood monocytes. Finally, CD4 ligation by MHC-II increases the susceptibility of blood-derived monocytes to HIV binding and subsequent infection. Altogether, our studies have identified a novel function for the CD4 molecule on peripheral monocytes and suggest that a unique set of events that lead to innate immune activation differ between humans and mice. Further, these events can have effects on HIV infection and persistence in the macrophage compartment.
Importance:
The CD4 molecule, as the primary receptor for HIV, plays an important role in HIV pathogenesis. There are many cell types that express CD4 other than the primary HIV target, the CD4(+) T cell. Other than allowing HIV infection, the role of the CD4 molecule on human monocytes or macrophages is not known. We were interested in determining the role of CD4 in human monocyte/macrophage development and function and the potential effects of this on HIV infection. We identified a role for the CD4 molecule in triggering the activation and development of a monocyte into a macrophage following its ligation. Activation of the monocyte through the CD4 molecule in this manner increases the ability of monocytes to bind to and become infected with HIV. Our studies have identified a novel function for the CD4 molecule on peripheral monocytes in triggering macrophage development that has direct consequences for HIV infection.
Insights
Human monocytes express CD4, which when activated by MHC-II, drives differentiation into macrophages. This CD4 activation also increases monocyte susceptibility to HIV infection, revealing a new role for CD4 in innate immunity and HIV pathogenesis.
Area of Science:
- Immunology
- Cell Biology
- Virology
Background:
- Human monocytes express the CD4 molecule, a characteristic not common in other species.
- The specific role of CD4 in human monocyte development and function remains largely unknown.
- CD4 is a primary receptor for HIV, crucial in HIV pathogenesis, beyond its role in CD4(+) T cells.
Purpose of the Study:
- To elucidate the function of the CD4 molecule in human monocyte development and differentiation into macrophages.
- To investigate the impact of CD4 ligation on intracellular signaling pathways within monocytes.
- To determine the effect of CD4-mediated monocyte activation on HIV binding and infection susceptibility.
Main Methods:
- Investigated CD4 activation via interaction with major histocompatibility complex class II (MHC-II).
- Analyzed cytokine expression and macrophage differentiation.
- Utilized inhibition of MAPK and Src family kinase pathways to assess signaling.
- Examined CD4 ligation by MHC-II on activated endothelial cells.
- Assessed HIV binding and infection rates on monocytes.
Main Results:
- CD4 activation by MHC-II triggers cytokine expression and monocyte differentiation into macrophages.
- CD4 ligation induces intracellular signaling, with MAPK and Src pathways being critical for differentiation.
- Interaction with activated endothelial cells promotes CD4-mediated macrophage differentiation.
- CD4 ligation by MHC-II enhances monocyte susceptibility to HIV binding and infection.
Conclusions:
- Identified a novel function for CD4 on human peripheral monocytes, driving macrophage development.
- Demonstrated that CD4-mediated monocyte activation has direct implications for HIV infection and persistence.
- Highlighted species-specific differences in innate immune activation pathways between humans and mice involving CD4.
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