HMC3

The Human Microglial Clone 3 (HMC3) cell line was developed in 1995 by Professor Tardieu's team through the SV40-dependent immortalization of microglial cells from human spinal cord and cortical tissues, obtained from embryos aged between 8 to 12 weeks. These primary cells, characterized by slow division and complex morphologies, were initially cultured for 10-15 days before immortalization. The HMC3 cells maintained several key features of primary microglia, such as a diverse expression of myeloid markers like CD68, CD11b, and CD14, though the expression levels varied notably with the choice of primary antibody, particularly for CD68.

Following immortalization, the HMC3 cells exhibited enhanced proliferation rates, with doubling times between 24 and 48 hours, while preserving many phenotypic and morphological characteristics of their primary counterparts. Notably, there was a higher proportion of CD68 EBM/11-positive cells and a reduction in phagocytic activity compared to the primary cells. Stability in antigenic expression was confirmed across 35 passages, with the cells remaining positive for NSE, CD68, and CD11b, but negative for CD14, MHCII, and CD4 under baseline conditions. However, exposure to interferon-γ (IFNγ) elevated MHCII expression, aligning more closely with primary culture responses to the same treatment.

Functionally, the HMC3 line distinguished itself by producing higher levels of interleukin-6 (IL-6) under basal conditions compared to other clones. Despite this, a direct comparison with primary microglial cells' cytokine production remains challenging due to methodological differences. The response to lipopolysaccharide (LPS) stimulation in these immortalized lines appeared diminished relative to primary cultures. Consistent with primary microglial characteristics, the HMC3 and other cloned lines did not produce tumor necrosis factor-alpha (TNFα), either spontaneously or following pro-inflammatory stimulation, highlighting a specific trait of human embryonic microglia.