I am using the book class and I wrote all the parts, sections, subsections as
\section{My Section Is Like This}
that I produce something like this
My Section Is Like This
My editor asked to write something like this:
My section is like this
I believe that I have to introduce a command like the one in capitalising-first-letter-of-each-word-in-section-headings-using-book-class:
\let\svsection\section
\def\section#1{\svsection{\titlecap{#1}}}
that does not solve my problem
or
something like that
\sectionfont{\scshape\MakeTextLowercase}
that produces
my section is like this
The problem is how to capitalize only the first letter of the sentence for all sections, subsections, subsubsections, but I have not been able to find it.

\section{}(in the source) to be capitalized for one reason or another, you can ignore this comment. – T. Verron Nov 24 '14 at 12:46