Aggregates/clumped cells

Undifferentiated cell cultures. Aggregate clumps of cells on solid media (callus) or in liquid media (suspension)... 

The clumping and aggregation of cells from suspensions in culture media to form masses is well known, but the resultant aggregates except for rouleaux formation by erythrocytes, are normally rather random as to their organization. The aggregates so formed, moreover, may or may not be weakly adherent, a matter which depends strongly upon the fields. 

AGGLUTINATION. The combination or aggregation of particles of matter under the influence of a specific protein. The term is usually restricted to antigen-antibody reactions characterized by the clumping together of visible cells such as bacteria orerythrocytes. 

Fig. 8.8. By looking at the peak at the 6C and 8C positions (aggregates of three and four cells), software algorithms use this information to estimate the contribution of clumps of two cells to the peak at the G2/M (4C) position. The graph at the right indicates the software estimation of these aggregated cells. The graph at the left indicates where these cells fall on a plot of signal area versus signal width.

When plated onto untreated dished F9 cells proliferate rapidly and form clumps of necrotic spheres by 4-8 days. In the presence of 5x10-8M retinoic acid (supplied from a stock of 1 mg/ml in DMSO) proliferation and aggregation occurs but, by about 5 days, embryoid bodies are formed which remain stable for more than 25 days (Adamson and Grover, 1983). It is in the early stages that differentiated functions are first expressed and alpha foetoprotein can be detected in the outer cells of the embryoid bodies at 6-8 days depending on the initial seeding density. There is increased production of laminin at 2 days. 

Multicellular microbial growth, especially fungal, often forms large cell aggregates such as mycelia, clumps, or pellets. Intraparticle diffusional resistances in these systems may be important and can lead to anaerobiosis. 

Negatively charged acylneuraminic acid residues impart a certain strength to cell membranes because of their mutual repulsion, and influence the mutual adhesion of cells in the organ structure. Whereas neuraminic acid allows the aggregation of embryonal muscle cells of the hen, presumably via Ca bridges, it prevents spontaneous clumping of blood platelets, and it so opposes any undesirable formation of blood clots. 

Care must be taken not to overtrypsinize the cells when removing them from the tissue culture surface. The 2.2.15 cells are sticky and have a natural tendency to clump. Aggregated cells do not grow well and are difficult to count. The 2.2.15 cells also perform better in reseeding and cryopreservation procedures if they receive fresh medium 24 h before trypsinization. 

In vitro studies indicate that synthetic A 3i 2 (A(342) can form insoluble aggregates and cause neurotoxicity after incubation for several days (Forloni et al., 1996). These A(342 assemblies may be stained by Congo red and Thioflavin S, similar to those observed in the AD brain (Jarrett and Lansbury, 1993). Both APi o (A(34o) and A 42 are formed intracellularly, but exert damaging effects when transported outside of cells. A 42 is more hydrophobic and toxic than AP4o, and its fibrils clump together to form amyloid plaques (Lue et al., 1999). Although A. 42 is the abundant Ap form in neuritic plaques, AP40 is more abundant in cerebrovascular plaques (Lue et al., 1999). 

In the control cells one can easily spot two very prominent actin structures (i) stress fibers that run along the lower, substrate-facing membrane interconnecting two sites of cell-substrate adhesion and (ii) the junctional actin ring that follows the cell periphery and stabihzes cell-to-cell jimctions. After exposure to CD both actin structures change dramatically. Instead of stress fibers and an actin belt around the cells, there are only actin aggregates that look like clumped monomeric actin without any filamentous structure. Thus, within 100 min of exposure time the actin filaments are disassembled. However, the cells remain spread and anchored to the growth substrate, so that after CD treatment there is still a confluent cell monolayer on the surface. 

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