deez nutz

one of my glaring weaknesses as a medical student (and as a person, really) is my pride. there are certain student-ish things i have historically refused to do--reread my notes, use a highlighter, write flash cards, etc. in the course of the past year, however, i've humbly had to break every one of these personal rules in order to manage the sheer bulk of material we have to learn. every rule, that is, except one: the no flash cards rule.

i should qualify this statement first and admit that i have cut 200 blank cards and have even written up two cards--one for choleragen and one for hereditary angioneurotic edema. to this day, those two cards remain unflipped, and therefore i don't count them as flash cards, i.e. they haven't been flashed.

still, as a result, i have abstained from flash card usage all year, often to my detriment. and in no instance was this detriment more obvious than when i was studying immunology. immunology became the bane of my existence because of its insistence on using nonsensical letters and numbers to describe everything that happens within it. the classic, most glaring example of this is the collection of cell surface molecules called CD molecules. even the deceptively simple "CD" name already presents a baffling challenge. call up a med student friend and ask her or him what "CD" stands for, and i bet you my tuition that your friend won't know (answer: clusters of differentiation, which, of course, is no more helpful than CD).

moreover, there are well over 200 of these CD molecules, approximately 1/6 of which we're expected to know, and none of which have useful, descriptive names, unless you naturally think "CD16" screams "phagocytosis." any normal student faced with the task of memorizing 40 CD molecules and their respective functions would head straight to a pile of blank flash cards or think of yet another corny mnemonic to sort everything out. unfortunately, i have neither the discipline nor the cleverness to do either, and so i'm simply going to list the relevant CD molecules below. next entry i promise to use more metaphors.

T-cell markers (CD2-8):

CD2
CD3 - part of the signal transducing complex that associates with the alpha/beta T-cell receptor (TCR, which cannot signal on its own)
CD4 - the receptor for class II major histocompatibility complexes (MHC). CD4 possesses no signal transducing function.
CD5
CD7
CD8 - the receptor for class I MHC. CD8 also does not possess any signal transducing function.

CD28 - provides a critical second signal for activation of T-cells. if the antigen presenting cells do not express the appropriate counter-ligand (CD80 or CD86), T-cells may be anergized (rendered "blind").

myeloid lineage markers (CD11-18):

CD11b
CD13 ]
CD15 ]--- elevated levels of these indicate myeloid leukemia
CD33 ]

B-cell markers (CD19-low 20's):

CD19 - deficiency in CD19 indicates agammaglobulinemia (e.g. low IgG)
CD20
CD21 - also found on follicular dendritic cells
CD22
CD23

CD10 - aka CALLA (common acute lymphoblastic leukemia antigen), CD10 is found on pre B-cells and hence indicates acute B-cell leukemia when detected in high levels. functionally, CD10 is a protease that helps immature B-cells navigate through the extracellular matrix.
CD40 - provides a critical second signal for activation of B-cells, in particular for immunoglobulin class-switching (IgM --> IgE) and for affinity maturation.

natural killer-cell markers:

CD2
CD7
CD8 - expressed at much lower levels than in cytotoxic T-cells
CD16
CD56

monocyte markers:

CD4
CD13
CD14

miscellaneous CDs:

CD32 - neutrophils, monocytes/macrophages, B-cells
CD34 - blasts
CD45 - all white blood cells
(CD45RO - memOry cells)
(CD45RA - nAive cells)
CD64 - monocytes/macrophages