FIGURE 1.1

Haematoxylin and eosin stained section of the parotid allowing the serous cells (top right), mucinous cells (left) and salivary duct (lower right) to be readily distinguished.

FIGURE 1.2

A section of renal glomerulus stained by haematoxylin and eosin. The nuclei have affinity for the basic dye haematoxylin and are blue. The cytoplasm has more affinity for the acidic dye eosin and is pink. This technique has not changed significantly in well over a century.

FIGURE 1.3

Electron micrograph showing the ultrastructure of a glomerulus. The increased detail is apparent even at this low power.

FIGURE 1.4

The principles of immunohistochemistry. The aim of the technique is to identify any cell bearing a specific antigen. The cell in the centre has antigens on its surface which are recognized by antibodies, often raised in mice, directed against that antigen. These are the primary antibodies. To demonstrate where these antibodies have bound, a secondary antibody is applied to the section. This antibody is raised in another species, e.g. rabbit, and directed against the Fc component of the primary antibody and therefore binds to it. An enzyme or fluorescent label is bound to the secondary antibody so that a coloured signal is produced. The cells on the left and right bear different surface antigens which are not recognized by the primary antibody and so no signal is produced in relation to them.

FIGURE 1.5

Interphase fluorescence in-situ hybridization (FISH) on a lymphoma using the IGH/CCND1 dual fusion probe (Vysis). (A) Normal pattern showing two green signals representing IGH on chromosome 14 and two red signals representing CCND1 on chromosome 11. (B) Abnormal pattern in a mantle cell lymphoma showing a single green IGH signal, a single red CCND1 signal and two fused signals representing the two derived chromosomes involved in the t(11;14) translocation. (For more information on the probe used see www.vysis.com/AnalyticSpecificReagents(ASR)_59424.asp
(Part # 32-191017.)

FIGURE 1.6

Gene expression microarrays were developed in the mid-1990s and have become a powerful tool to study global gene expression. Real time polymerase chain reaction (RT-PCR) is used to generate cDNA from mRNA extracted from test and control samples. The test and reference cDNAs are labelled with different fluorochromes, in this case represented by the red and green circles. These samples are then competitively hybridized to an array platform that comprises representations of known genes or expressed sequence tags (ESTs) which have been spotted onto a solid support, usually glass or nylon. The presence of specific cDNA sequences in each sample can then be determined by scanning the array at the excitation wavelength for each fluorochrome, with the ratio of the two signals providing an indication of the relative abundance of the mRNA species in the two original samples. Although spotted microarrays are still in use today, the market is now dominated by one-colour platforms such as the Affymetrix GeneChip in which a single sample is hybridized to each array. Gene expression microarrays have been used in numerous applications including identifying novel pathways of genes associated with certain cancers, classifying tumours and predicting patient outcome.

FIGURE 1.7

Adenocarcinoma of colon. Malignant glandular structures (arrows) have invaded the wall of the bowel and have almost reached the peritoneal surface (arrowheads).

FIGURE 1.8

Secondary (metastatic) adenocarcinoma of colon in a lymph node. Two malignant glands can be seen, with surviving node to the right. A tumour that has reached nodes by the time of diagnosis has a worse prognosis.

FIGURE 1.10

This breast aspirate shows cells with a high nucleus:cytoplasmic ratio and loss of cohesion indicating malignancy.