The MRC-5 cell line was initiated by J. P. Jacobs in the mid-1960s from the pulmonary tissue of an aborted 14-week-old male human fetus. The fibroblast line exhibits adherent growth to glass and polymer culture dishes and can double in population size more than 40 times before senescence occurs.

MRC-5 cells are negative for the enzyme reverse transcriptase and are known to be susceptible to a number of viruses, including herpes simplex, vesicular stomatitis (Indiana strain), and poliovirus 1. The MRC-5 line is a popular cell line often used in a variety of applications, such as virology-related transfection experiments, cytotoxicity assessments, and the development of vaccines.

In recent years, MRC-5 cells have been particularly important in the production of smallpox vaccines. Smallpox was virtually eliminated from the United States in the late twentieth century, but the increasing threat of biological warfare has led to escalated vaccine production. Smallpox vaccinations are not mandatory, but the increased stores of the vaccine could greatly stem damage from the disease in the case of an outbreak. This is because in addition to conferring resistance to infection, smallpox vaccines can decrease the seriousness of illness in patients that were not vaccinated prior to virus exposure.

The culture of human fetal lung fibroblast cells presented above was stained with Alexa Fluor 350 conjugated to the lectin concanavalin A, which selectively binds to alpha-mannopyranosyl and alpha-glucopyranosyl residues (primarily in the endoplasmic reticulum). Alexa Fluor 568 conjugated to phalloidin and SYTOX Green were also used to label the culture, targeting filamentous actin and nuclear DNA, respectively. Images were recorded in grayscale with a 12-bit digital camera coupled to either a Nikon E-600 or Eclipse 80i microscope equipped with bandpass emission fluorescence filter optical blocks. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.

MRC-5 Cell Culture Labeled for Peroxisomal Membrane Proteins and Histones with Immunofluorescence - The peroxisomes and histones present in the MRC-5 fibroblast cell culture illustrated in this section were immunofluorescently labeled with Alexa Fluor 488 conjugated to goat secondary antibody fragments directed against rabbit primary antibodies to peroxisomal membrane protein 70 (PMP 70) and Texas Red conjugated to secondary antibody fragments against mouse primary antibodies to nuclear histone proteins.

Visualizing the Golgi Complex and Nucleus in Fetal Lung Fibroblast Cells - In order to examine structural features of the Golgi complex and nucleus, a log-phase culture of MRC-5 cells was fixed, permeabilized, blocked with normal goat serum, and then treated with rabbit anti-giantin (Golgi protein) primary antibodies followed by goat anti-rabbit secondary antibodies (IgG) conjugated to Alexa Fluor 568. Cell nuclei were counterstained with Hoechst 33258.

Histone and Peroxisome Distribution in MRC-5 Cell Cultures - In a double immunofluorescence experiment, the adherent monolayer culture of MRC-5 cells presented in this section was fixed, permeabilized, blocked with 10 percent normal goat serum, and treated with a cocktail of mouse anti-histones (pan) and rabbit anti-PMP 70 primary antibodies, followed by goat anti-mouse and anti-rabbit secondary antibodies (IgG) conjugated to Texas Red and Alexa Fluor 488, targeting cell nuclei and peroxisomes, respectively. The cytoskeletal actin network was counterstained with Alexa Fluor 350 conjugated to phalloidin.

Targeting Mitochondria and the F-Actin Network in Human Fetal Lung Cells - The mitochondria present in a culture of MRC-5 fibroblasts were targeted with MitoTracker Red CMXRos, a derivative of X-rosamine. In addition, the culture was labeled for nuclear DNA and the cytoskeletal F-actin network with SYTOX Green and Alexa Fluor 633 conjugated to phalloidin, respectively.

MRC-5 Fibroblasts Triple Labeled with Alexa Fluor 350, Texas Red, and Alexa Fluor 488 - The adherent monolayer culture of MRC-5 cells depicted in this section was fixed, permeabilized, blocked with 10-percent normal goat serum, and then treated with a cocktail of mouse anti-histone and rabbit anti-PMP 70 (peroxisomal membrane protein) primary antibodies followed by goat anti-mouse and anti-rabbit secondary antibodies (IgG) conjugated to Texas Red and Alexa Fluor 488, respectively. Alexa Fluor 350 conjugated to phalloidin was utilized to counterstain the F-actin network.