Cell Biology and Tissue Culture: Biology of Cultured Cells and HeLa

Fundamentals of Cell Morphology in Tissue Culture

• Definition of Morphology: In the field of biology, morphology is a specialized branch of bioscience that focuses on the study of the form and structure of organisms, specifically examining their unique structural features.
• Role in Cell Culture: Regularly examining the morphology—defined as the shape and appearance of cells—is fundamental to the success of cell culture experiments.
• Importance for Technicians:     * Acquaintance: It allows the researcher to "get to know" the specific cell line.     * Routine Monitoring: Looking at cells using an inverted microscope is a daily standard procedure.     * Health Assessment: Visual cues enable a technician to determine if cells are unhealthy, require feeding (nutrient replacement), or need splitting (subculturing/passaging).     * Risk Mitigation: Proper morphological monitoring can save an experiment from failure or prevent a major contamination outbreak.
• Visualization Tool: The Phase Contrast Microscope is the primary tool used. It is a type of light microscopy that enhances the contrast of transparent and colorless objects by influencing the optical path of light.

Cell Growth Modes and Growth Patterns

• Growth Form Categories: Cell cultures generally take one of two forms based on their growth mode, which typically reflects the tissue of origin:     * Adherent Cells: These grow as a monolayer attached to the surface of a tissue culture flask. They are typical of cells derived from solid tissues, such as the lungs or kidneys.     * Suspension Cells: These grow as single cells or small free-floating clumps. These are typical of cells derived from blood, such as leukemia or lymphoma cell lines.
• Confluence and Confluency:     * Confluence Defined: A measure indicating the number of cells attached to a substrate, specifically the percentage of the dish or flask surface covered by cells.     * Confluent Monolayer: A state where the substrate of the culture vessel is completely covered with cultured cells, leaving no remaining room for the cells to grow as a monolayer.     * Over-confluent State: Characterized by unclear cell edges and large areas where cells begin growing on top of each other, resulting in the loss of the monolayer structure.     * Visual Benchmarks: Cells are typically assessed at specific confluency intervals, such as $10\%$, $20\%$, $30\%$, $50\%$, $70\%$, $80\%$, $90\%$, and $100\%$.

Detailed Classification of Attached Cell Types

• Fibroblasts:     * Function: The principal active cell of connective tissue, responsible for producing high volumes of extracellular matrix (ECM) proteins, including collagen, glycosaminoglycans, and proteoglycans.     * Immune Role: They act as immune regulators by recruiting immune cells to amplify inflammation.     * Morphology: Adherent and irregularly shaped. They appear bipolar (two extensions) or multipolar (many extensions) and elongated. In heavy cultures, they frequently form distinct "swirls."     * Applications: Used to model disease mechanisms, study cell-cell interactions, and test therapeutics for chronic inflammation.

• Epithelial Cells:     * Distribution: They line the inner surfaces of the body, including the respiratory tract, gastrointestinal tract, and the tubules of the nephron.     * Functions:         * Protection: Skin epithelium guards against injury and bacteria.         * Absorption/Secretion: Specialized for absorbing nutrients in the gut or secreting mucus, enzymes, and hormones in glands.         * Structure: Arranged in simple (single) or stratified (multiple) layers.     * Morphology: These are attached cells that appear flattened and many-sided (polygonal). They grow in sheets or patches rather than spreading individually.

• Endothelial Cells:     * Distribution: They form the tunica intima, the thin layer lining the interior of blood vessels.     * Characteristics: They provide a smooth, anticoagulant surface that acts as a selective filter for fluid, gases, molecules, and immune cells.     * Sources: Can be isolated from the human aorta, umbilical vein (HUVEC), and pulmonary or coronary arteries.     * Morphology: In culture, they maintain a characteristic single-layer growth pattern with a "cobblestone" monolayer appearance at stationary density.

• Neuronal Cells:     * Function: Responsible for transmitting and receiving neurotransmitters (chemical messengers) between brain cells.     * Classifications: Can be sensory neurons, motor neurons, or interneurons.     * Culture Challenges: Extremely difficult to culture because mature neurons do not undergo cell division. Research often utilizes Neural Progenitor Cells (e.g., astrocyte lineage reporter lines like XCL-1 GFAPp-Nanoluc-Halotag).

Suspension Cell Characteristics: Lymphoblasts

• Origin: Hematopoietic (blood cell) origin.     * Growth Mode: Do not attach to substrates; they remain in suspension.     * Morphology: Spherical shape.     * Lymphoblastoid Cell Lines (LCLs): These are immortalized B lymphocyte cultures, often created by transforming human peripheral blood lymphocytes with the Epstein-Barr Virus (EBV). They provide a stable source of DNA and human cells for genetics and drug screening.     * Example: The Raji line, established in 1963 by R.J.V. Pulvertaft from the Burkitt's lymphoma of an $11\text{-year-old}$ Black male.

Summary Table of Common Cell Lines

Pathological Morphology: Viral Infection Example

• Example Case: Human corneal epithelial cells infected with Herpes Simplex Virus-1 (HSV-1).
• Normal State: Cells exhibit a healthy "cobblestone" appearance.
• Cytopathic Effect (CPE):     * At $8\,\text{hours p.i.}$ (post-infection), the space between infected cells increases noticeably.     * Morphological changes progress significantly by $12\,\text{hours}$ and $24\,\text{hours}$ post-infection.

Historical Timeline of Tissue Culture

• 1907: Isolated nervous cells from the spinal cord.
• 1912: viable cell cultures maintained for longer periods using asepsy and nutrients.
• 1951: Establishment of the HeLa cell lineage.
• 1956: Observation of cell agglomerates on rat-tail collagen.
• 1975: Implementation of 3D cell culture using human progenitor cells.
• 1980–1990: Development of "Organoids" representing neuroblastoma and lung tissue.
• 1993–1997: 3D culture utilized for transplantation purposes (cornea and skin).
• 1998: Successful isolation of human Embryonic Stem Cells (ESCs).
• 2006: Establishment of induced Pluripotent Stem Cells (iPSCs).
• 2009: Description of "mini-guts" (small intestine organoids).
• 2012: Establishment of induced Neural Stem Cells (iNSCs).

The HeLa Cell Line and Henrietta Lacks

• Origin Story: Henrietta Lacks was an African-American mother of five who visited Johns Hopkins Hospital in 1951 for vaginal bleeding. Dr. Howard Jones discovered a malignant cervical tumor.
• The Discovery: A biopsy of her cancer cells was sent to Dr. George Gey's lab. Unlike previous samples that died quickly, Mrs. Lacks' cells doubled every $20\,\text{to } 24\,\text{hours}$.
• Scientific Breakthroughs: HeLa was the first immortal human cell line, allowing for tests on human tissue outside the body.
• Historical Research Applications:     * Space Race: Sent to space to study the effects of zero gravity on human cells.     * Nuclear Testing: Used to determine radiation effects from nuclear explosions.     * Commercial Industry: Used by the beauty industry to test cosmetic side effects.     * Medical Science: Used to study genetic mutations, develop cancer therapeutics, and create treatments for infectious diseases.
• Biological Characteristics:     * Rapid Proliferation: They grow abnormally fast compared to typical cancer cells.     * Telomerase Activity: HeLa cells possess an active version of telomerase during division. This prevents the shortening of telomeres, which is the process usually responsible for aging and cell death.     * Hayflick Limit: By maintaining telomere length, these cells circumvent the Hayflick Limit, the finite number of divisions a normal cell can undergo before becoming senescent.     * Genetic Profile: Horizontal gene transfer from Human Papillomavirus 18 (HPV18) created a unique HeLa genome.     * Chromosomal Composition: They have a "hypertriploid chromosome number ($3n+$\)." This results in a total of $76\,\text{to } 80\,\text{chromosomes}$ per cell, contrasted with the normal human diploid count of $46$.

Laboratory Documentation and Passage Number

• Passage Number: A critical metric indicating the total number of times a specific cell line has been sub-cultured, passaged, or split since its isolation.
• Log Maintenance: Proper laboratory records must include accurate terminology, annotated images, and compliant logs to track cell condition and experimental timing.