Here is a summary table (already needing to be updated to ferret pix=365; guinea pix=664 with animals being n=61; rat pix=44, n=3: for a new total number of micrographs of 1456), which I could not resist making “pretty”. It does give you an idea of how many electron micrographs have been perused in order to make some statements about whether this protein granule is a part of the regular surfactant machinery or whether it represents something in the way of an “overproduction of protein – hypothetically, surfactant protein A) in a disease state. (I am leaning toward this view). (115 total, 12 species, at least two dozen obscure experimental groups, ages and controls mixed in, three types of processing fixatives, at least three embedding compounds, silver and gold sections, standard uranyl acetate lead citrate staining, and half a dozen different electron microscopes utilized over 30 years, and tissues from at least a dozen different investigators (their materials plus mine).  Well over 1000 type II cell images examined in detail.

Going back over 114 micrographs of alveolar type II cells in the lungs of dogs (n=9; mostly controls from other experiments or ozone treated, taken expressly for lung morphology looking for ICBs) I found several reasonable occurrences which are montaged here. These images are cropped from micrographs of various magnifications, and while I did enhance contrast on some light ones, no dust and scratches or other photoshop applications were used.  There are some pretty nasty micrographs here, but this is an unbiased sampling of all the ICBs that I found in all the dog tissues that I had photographed in the 1980s.  At least three fixation fluids were used: Modified Karnovsky’s, a glutaraldehyde paraformaldehyde mix, and direct osmium.  It seems that the direct osmium preserved the periodicity in the granules better than the aldehydes, but the micrographs were not as informative overall. White arrows point to the granules (ICBs).  Only in two micrographs were the granules seen in parallel RER profiles, one with 2 stacks and one with 3.

The most important observation here, aside from the more central dense line in the granules, is there apparent increased density on the limiting RER membranes, the paucity of ribosomes from the parallel edges, the presence of ribosomes on the leading edges, and a very easy to see “rigidity” to the whole granule when compared to other nearby RER profiles which have variable widths , and also NO central or multiple parallel densities within. Also, a fixed width to the type II cell granule (ICB) appears to be roughly equivalent to about 4 or 5 ribosomes (nearby on the same image) still seems to be about 100nm, and counting the periodicity in the middle and upper and lower densities along the long axis of the granule might be about 7 dots per 100 nm, which actually gives the protein within and the linear periods in both x and y axes similar dimensions: 7 bands high, 7 periods in length.  One would be remiss not to mention that tubular myelin is kind of a “square tubular lattice” so there might be a connection.

Still searching, here, for clues as to what types of organizational patterns can appear in the rough endoplasmic reticulum of alveolar type II cells. It becomes apparent that not all species have these organizational things, the intracisternal bodies, or granules. The hamster comes close, perhaps, and if this is not my imagination, I have highlighted a periodicity (mostly dotted) within a few profiles of RER in the cytoplasm of an alveolar type II pneumocyte.  There are some obvious differences between this organization (if it is not artifact) and the granules that appear in the guinea pig, ferret, and dog type II cells that are noteworthy. 1) if the dotted appearance is real, then it is perpendicular to the long axis of this RER profile, and 2) if this is a surfactant protein organization at all, then it doesn’t demonstrate the same periodicity as the other three species.  This doesn’t mean of course that it is not a surfactant protein, ’cause it likely is. Even at the widest part between rows of “dots” there is probably not 100 nm…  maybe 80 or 90, so that puts the size a little off.  Ribosomes in blue can be used as a reference to approx 20-30 nm diameter.

Yellow orange body is the RER profile with dots,  purple-blue, ribosomes for comparison in size.  (neg 7287 block 24716 hamster, born 9 1981, presumably female, animal 2 of three, @ 1.5 yr old.

Lamellar body in an alveolar type II cell has surfactant-like-tubular-myelin grid pattern. This was found in an electron micrograph of a ferret type II cell (neg 9872, block 23462, ferret # 7, control, 6 10 1982). This particular lamellar body is unusual in that within the lamellar structure, there is a grid like pattern which is normally seen only in the alveolar space. While, according to the literature, alveolar type II cells can internalize mature surfactant from the alveolar space, this doesnt anatomically seem very likely to me as an explanation for this particular structure.  I thought it was unusual enough to post. I put a bounding box and a drop shadow around the area of interest.  The grid inside has at least 4 partitions horizontally as well as vertically.  Surfactant protein A is likely responsible for the grid (according to consensus) though this is usually in the alveolar space. This mineature tubular myelin was described in a book, ed Jacques Bourbon I think, which was reported to be about 1/3 the size of tubular myelin in the alveolar space.

Here are two reference images for the above micrograph to give approximate sizes. Regular tubular myelin has a side to side distance of something around 100 nm, whereas this intra-lamellar-body mineature tubular myelin sample is about 60 nm?  Ribosomes are 25-30 nm (black circles)